A lot of the recentness of some of the top songs here is just due to the fact that the audience for pop music now is so much bigger than it’s ever been.
The official video for “Uptown Funk” has 3.4 billion views on YouTube. There weren’t even that many people living in Elvis’ day, let alone people with access to American pop music.
#14 is the first one I don’t recognize. I’m sure I’ve heard it, but it sound like pretty generic pop R&B to me. Probably just blended into the background. #37 is the next one I don’t know, and the first that I don’t think I’ve ever heard before.
Sorry to defy your world view, but I have never heard them until just now. And I do all those things. Apparently just not the TV shows, movies, commercials or stores that you do.
Of course this is the SDMB, where people think whatever they experience is the only valid experience in the world.
Oh, I didn’t recognize it by name, either (there’s actually a good number I didn’t know by name), but within hearing the first second or two of the clip, I instantly knew the song. If the question is what was the first song I didn’t recognize by name, then “Closer” would be my answer, but I’ve heard that song like a zillion and a half times; just never knew the name of it.
To be honest, this is a quality which is universal to humankind. Just ask my daughter, and she’s not even on the Dope. 
Every time I hear it, I think of the Simpsons: https://www.youtube.com/watch?v=4OhkhBwrK_w
There were a handful of songs I didn’t recognize in the top 100, mostly in the soul/R&B category.
I didn’t count them to be exact, but I’m guessing that I have NEVER heard at least one-third of these songs. (I’m in my mid-60s and listen to classic rock almost exclusively.)
It would be interesting to see a similar list created based on the %age of audience/market at the time the song was popular. For example, a song released in 1968 might have represented 1% of all singles sold that year, but still have sold fewer than a single that sold twice as many in 1998 that was only 0.5% of the singles sold that year. In my list, the 1998 single would be ranked much lower than the 1968 single, even though the 1998 single sold many more copies.
In spite of the fact that I haven’t paid much attention to the Billboard charts since the mid-1980s, I’m surprised that the highest-ranked song that I didn’t recognize was all the way up at #5. I pulled up that Leann Rimes song up on YouTube to see if it was one of those songs I’ve heard enough to recognize but never knew artist/title (like LMFAO at #6), but nope, just some generic sappy love ballad that I couldn’t discern from any other of the legions of generic sappy love ballads out there.
Looking into the additional details Billboard provided, I see that it peaked at #2…how the hell is that ranked higher than songs that had been #1 for months? This one is definitely my answer to both questions 1 and 3 in the OP.
Elsewhere in the top 20: 7, 9, 13, 14 and 16 are all artists I’ve heard about a lot but couldn’t place the songs.
As to question #2, I was somewhat surprised that “Don’t Stop Believin’” by Journey was nowhere on the list of 600, though that was more of a pop-culture hit long after it was new. No other Journey songs made the list, not even “Open Arms” which I remember being a pretty big hit in its time (which their Billboard page confirms as their best-charting song with a top position at #2).
The same could be said for “Africa” by Toto, but at least they have “Rosanna” on the list…which is also somewhat baffling since “Africa” actually was a #1 hit while “Rosanna” peaked at #2.
#9 - “Shape of You” by Ed Sheeran
I simply do not understand his popularity. Auto-tune city.
What a complete pile of shite, songs that are poor covers of far better versions are in there, even when the cover is not as well known as the original.
Not one heavy rock song, almost no rock and roll, virtually no funk as played by funk artists, overly heavy reliance on Madonna and Adele, and not even their best material. Can’t see any reggae , no Bob Marley - really?
Entire genres of music are not included .
This list has zero credibility.
For what it is, a ranking of popular songs by Billboard magazine, who has ranked popular songs since 1958, and, of course, formed the basis of Kasey Kasem’s career, this list has all the credibility it needs.
What it’s not, as noted, is a selection of songs made by critics/musicians/etc. If death metal, for example, wasn’t popular enough to break the top 10, well, that’s why it’s not on this list.
It’s sad that there’s no indication on the website of exactly how they determined which songs were the “hottest” over the 60 years. I would, however, tend to agree with whomever posited that the methodology simply added up points based upon an inverted scale. Thus, a song that made #2 at the highest and was on the top 100 a lot of weeks might outpoint a song that made it to #1, but faded quickly. For example, the LeeAnn Rimes song, “How Do I Live” lasted a record 69 weeks in the Hot 100, and set records for time in the top-10 and top-5, but was stuck behind “Candle In the Wind (Princess Diana version)” by Elton John and Savage Garden’s “Truly, Madly, Deeply”.
The “credibility” is 100% reliance on what has been most popular (I think). That the masses have shit taste in music is unsurprising.
At least I assume this list was compiled from the Billboard chart numbers and do not rely on any subjective measure.
As an aside I was introduced to this good funk band recently (kind of a blend of funk/R&B/soul). If you like funk you might give them a listen. THIS is good music, much, much, much better than Ed Sheeran (to name one high on that list in the OP).
Mine is all the way up there with number 2, Smooth. I counted 25 more that I didn’t recognize before hitting item # 70 and getting bored.
A song selling many millions during its era of release is not nesassarily an indication of its popularity across generations.
Reason for this is that something selling 1 million in 1960 and getting to the top of the charts is not the same as selling 1 million in 1969, or a song selling 500k and getting to the top of the charts in 1980.
It depends upon the size of the market at the time, in addition its worth noting that sales across eras are not like for like, sales at one time were physical and did not include copies that were on albums, nowadays even ringtones count as sales. Things such as streaming count toward the rating of songs these days, and its hardly surprising that this list is heavily weighted toward modern means of music consumption.
So of we are going to rate songs, then some adjustment needs to be made to account for this.
Bohemian Rhapsody went back on the chart in 1992 because it was in Wayne’s World
The Billboard charts have made four major adjustments to how they measure the charts, from tabulating jukebox plays in 1958 to radio and sales in the 1960s-onward, to streaming in 2019. The various methods are weighted - 1 stream doesn’t equal 1 sale which doesn’t equal 1 radio play - but I haven’t the slightest idea what the formula is (I once heard 10 streams = 1 sale, but that was quite a while ago and I bet the ratio is more tilted nowadays, like 20:1, more).
This is all quite irrelevant. The issue isn’t total popularity numerically, it’s relative popularity. A song that was #1 for one week in 1958 is the equivalent of a song that was #1 for one week in 2017. They aren’t comparing sales/plays/streams/whatevers; they are comparing total time on the chart, weighted for the position each week.
If you think he’s bad on his own with that song, be thankful you aren’t regularly subjected to that song, the bad wedding song about loving some chick when she’s 70, and the duets with Justin Bieber AND Beyonce.
I do not begin to think that this represents relative popularity, although I accept that it purports to do this.
You only have to look at the relative positions and years of song release to understand how skewed this is toward stuff from post 2010 years.
Their metric is simply wrong, or rather they have it right in the sense that the Billboard 100 has always been marketing tool, and it makes little sense to further promote material whose revenue stream has largely dried up.