Because you don’t know if you just have an undeveloped palate for it, or if you really, truly won’t like it. Same thing with coffee, wine, spicy food, etc. Turns out I hated beer because the stuff people were serving in college was the cheapest, crappiest Light American Lager that a college student could afford. Once I eased my way into beers by going for the sweeter kinds first (Leinie’s Berry Weiss and Honey Weiss, then Dundee’s Honey Brown), I learned how to appreciate a good beer. Same way that I got into liking wine - started out on koolaid-like white zinfandels, and worked my way up into loving big Supertuscan reds.
For me it was social convenience - I acquired me beer taste over a stint as a receptionist in an engineering office in Sydney where at 4:30 PM sharp on Fridays I got to wander around distributing beer in an effort to keep the boys from leaving the office. It was convenient to make an effort to drink along with the boys, although there was also terribly sweet hard cider available. I prefer slightly bitter over terribly sweet so although I didn’t love the beer, I’d drink a bottle once every couple of weeks.
Then I went directly from there to Oregon where my social circle consisted of husband’s student musician friends. Beer by the pitcher (good beer at least!) was pretty much it, and the pubs aren’t necessarily licensed to sell anything harder. That’s when I discovered I actually like dark beer and now I quite enjoy any number of different beers.
But I’ve never tasted anything more commercially available than Sam Adams - i.e. your buds, millers, and I can’t imagine ever bothering to acquire that taste. Even Sam isn’t really robust enough to be thoroughly pleasant to me.
Never liked beer. My early exposure to it was the low-grade crap they serve at ballgames, which just smelled foul and sour and nasty to me, as did all the subsequent beers I was later exposed to. To this day, though I’ll suck one down now and then to be a sociable guy, I’m always thinking “Yecch! Shea Stadium, Yankee Stadium, Polo grounds, yecch,” the whole time.
I never liked beer, either, but like others here I eventually found it behooved me to develop a taste for it. The mixed drinks I was drinking when I was out for 6 hours or more at a stretch shooting pool and socializing were taking too big a toll on my tummy. (Plus I was sucking them down too fast because I liked the taste – I figured switching to beer would slow me down, since I didn’t really care for it). I found that Corona with lime worked as a good starter beer for me. Now I like either Corona or Yuengling lager. I can manage a Bass, and I rather like Negra Modela, but that’s about my full range at this point.
When I was a little kid, up until about maybe age 7, I liked beer and would sneak sips out of people’s cans if they were left sitting around. But as an adult I can’t stand the stuff. I’ve tried all different types: light, dark, in-between.
I am open to the possibility that somewhere out there there is a kind of beer I can tolerate, and in a certain sense I wish I liked beer because it would make a lot of social situations simpler (not because I need to be more buzzed, but because sometimes I want to go see a band in a bar, and the other drink choices are unappetizing, especially if I don’t want something sugary or caffeinated, and given the kind of red wine - my usual preferrred alcoholic beverage - that you can order in a lot of bars where music is played, you might as well order a glass of pureed tree bark). But I don’t know that I’m willing to waste a ton of money trying a bunch of things I’m likely to strongly dislike, so until that day comes I’ll sdtick to ordering tonic with lime, or cider if it’s available, or girly rum drinks.
(I do like a nice raspberry lambic once in a blue moon, though.)
I prefer bitter to sweet.
I love Killian’s, and I can’t eat really enjoy spicy chili or Mexican fare without Guiness. I have a girlfriend who also likes stout, and we make a meal out of a pint of warm Newcastle a couple times per month. Most sweet alcoholic drinks give me a headache- I don’t care for rum and the sweetest mixed drink I like is a perfect Margarita with a dish of olives on the side.
I also like unsweetened tea, spinach, beets, and only the darkest of chocolate. Beer isn’t an acquired taste for me- I liked it from the first sip.
I have to say that what I like most about beer is the quality of the high. If I don’t have a beer, I will make myself a black russian or maybe a martini, but they don’t quite do it for me. I suspect it has to do with the speed at which I drink the beer and the alcohol is introduced into my system. This is not to say that the taste is unimportant. I like all different types of beers, except the tasteless ones (tasteless, ice cold beers go down way too fast), but I did not begin to drink beer because of the taste.
An important lesson that I learned the hard way is that the quality of the high of the first beer cannot be improved upon by subsequent beers. A second beer, judiciously timed might extend the high a bit. After that the quality of the high (and sometimes your life) deteriorates rapidly.
Admitted beer snob checking in (best credentials-- lived in Ghent where the local beer store was the Hopduvel): If you really want to understand and give it a shot you’ll have to invest in something better than what you listed in the OP, none of which I would drink unless it were free and I were desperate. I mostly despise lagers like that. Fat Tire is at the very bottom end of decent-- it’s what we buy when we just need two cases right away. This might help explain your problem. I can’t speak for yellow lager lovers. Corona and Heineken and such are not my favorite type. And there are many bad, bad imports.
So to experiment, run out to the decent liquor store in town or import market and buy a Guinness in the can with the little cartridge in the bottom (not the bottle), a Chimay Tripel (beige label), a Hacker-Pschorr Hefeweizen, and. . . what’s your geographical location? Hard to tell what domestic micros would be available. And a Fullers London Pride. None of these should cost too much and will give you idea of range of types that are not yellow lager.
Bass is good stuff without doubt, but the most palatable beer that’s readily available is Sierra Nevada Pale Ale. If you try this stuff and you just don’t like it, then you don’t like beer. (It’s very mildly hoppy but sweet.) If you’re in the Milwaukee/Chicago area, Sprecher makes a great Amber and their Pub Ale is very nice, too, plus they make some awesome root beer, cream soda, and ginger ale.
Sam Adams is crap beer, barely above Miller/Busch/Coors on the scale of things. Plus all varieties seem to have the same nasty aftertaste, like they don’t clean their equipment. Call me a beer snot, but I just plain won’t drink it.
Maybe you’re just not a beer guy, though. Nothing wrong with that. Here, have a glass of some HP Cork Dancer Pinot. Nice stuff, in’it?
Stranger
Whoa, hossie! Don’t start him out on the top of the pyramid; let him work his way up. Next thing you know, you’ll be givin’ him a snifter of Middleton Very Rare without first introducing him to the nectar that is Black Bush, then drawing him in with Redbreast 12 Year. What, do you give your 16 year old the keys to a BMW M6? 
Stranger
Yep, beer is bitter. Lots of drinks (coffee and tea for example) are bitter.
Since I do not know where you are, I am hard-pressed to advise you, Freudian Slip**. At home I enjoy cold Rolling Rock in the small pony bottles. Wonderful stuff with just about the ideal dosage.
Now whiskey, that I do not understand.
Great choice and one of my favorites when I cannot get a Bass. I love Hacker-Pschorr Oktoberfest, but this is the only time of year that it is available of course.
Jim
mmmm beer!!
Homeresque type voice
You, sir, are cruel. 
There have been some good beers mentioned so far, but Sierra Nevada is so far from “mildly hoppy” that I had to step in and give Stranger a yellow card.
Sierra Nevada is all about the hops, man! For a novice, I’d recommend trying some of the excellent bocks being produced around the country, especially the golden ones. But the OP stated that even they tasted bitter, so that leads me to state thet they should probably drink wine instead. No biggie, just leaves more beer for the rest of us.
BTW, today’s selections at Casa Silenus are the aforementioned Sierra Nevada, Karl Strauss Red Trolley Ale and Sam Adams Octoberfest. It’s not quite time to dive into this year’s Celebration Ale, but I have a case on hand when the time arrives.
I am not a fan of beer myself, but I’ll drink it if there’s nothing else. Lately I’ve discovered cider, which I like much better - yes, I have a sweet tooth, although oddly enough I’ll drink my coffee black most of the time. Our school pub serves Woodchuck apple and pear. If you think beer is too bitter, you might want to try cider instead. Strongbow isn’t bad either.
My bad. I consider it “mildly hoppy” for a pale, but looking at it I see it has an IBU of 37. But then, I thnk beers like the Pyramid Thunderhead and Stone IPA are the pinnacle of hoppy goodness, and the bitterness of Sierra Nevada is mild in comparison. I still think if you can’t like this, you won’t like beer. (Like capybara I can’t get much into flavorless “yellow lagers”, and I’m having to forcibly restrain my love of porter and stouts for the sake of the discussion.)
Ach, you just havne’t had the right exposure. A nice Irish whiskey, or an excellent not-too-peaty Scotch whiskey like Glenmorangie Port Wood Finish 12 Year with a drop or two of branch water will bring you 'round.
Stranger
You had to bring up Stone IPA, didn’t you? Now I have to go shopping!
I don’t know that I’ve ever had the Hacker-Pschorr Oktoberfest, come to think of it, but I’m always happy when the Spaten Marzen Oktoberfest is in season (which seems to be a substantial portion of the year). Sprecher makes an Oktoberfest that’ll knock every major import on its arse, though. Ah, the things I miss about Milwaukee.
Stranger
Get some for me. And some Hoegaarden Witbier while you’re at it. (Their Forbidden Fruit is better but I can’t find it anywhere, damnit.)
Stranger
Liquorama, in Upland. On your way home from work, get off of the 10 at Euclid. Go north to Foothill, and turn left (west). It’s catty-corner from Upland High School, back in the corner of a failed grocery mall. If they don’t have it, it’s unavailable in the US.