Perhaps the movies have given me the wrong impression, but I thought people very commonly wore hats in the past. Sure, you’ve got a lot of poeple wearing baseball caps but those tend to be people who, in the past, wouldn’t have worn hats at all. A few college students/artists wear newsboy hats.
Why did people stop wearing?
When did that change happen and where did it first happen?
1961, when JKF walked in his inaugural parade without a hat.
In the “swinging sixties,” hats were viewed as being a legacy of the older generation, and were dropped from being a standard part of a man’s wardrobe. They do seem to be coming back, but I happen to hate the skimpy brim styles the hipsters are wearing nowadays.
A lot of people point to JFK’s inauguration, claiming he didn’t wear a hat. I think he did have a topper, though, even if he didn’t wear it during the ceremony.
One thing is that car tops got lower in the '60s, leaving little room to wear a hat while driving. Perhaps that, combined with more people parking closer to their destinations, plus a mmore casual dress code diminished the desire to wear hats. I know that movies from the early-to-mid-'70s often depicted men in certain cities who wore hats, often a trilby or a porkpie – smaller hats than the traditional fedora.
EDIT: Snopes on Kennedy’s hat.
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Facts? To get in the way of a good story? Ridiculous.
True fact is that Oswald was in the pay of the International Milliners Associationl. 
I see plenty of hats here. Of course, the fact that it’s midwinter and they’re all tuques keeping our heads warm may have something to do with it.
This topic is a perennial favorite.
Check out Why did men’s hats go out of style? Will they ever come back? for a longer discussion. Especially my post where I tear into that Snopes article.
Here’s another long thread on hats and a really long one on formal dress in general.
I recently started wearing a hat. I have several and even got a old-fashioned Top Hat to wear at Christmas (but didn’t this past Christmas because I didn’t go to any formal parties.)
I have a black fedora and a gray Bowler. the Bowler is a tad too big and I can’t decide if I should try to shrink it or buy a new one.
As I’ve mentioned in other threads on hats, people have been claiming that they’re coming back in style for the entire twenty years I’ve been wearing them, on what seems like a bi-annual basis. But there’s never been a better time for a revival, because you no longer have to depend on a local store carrying a decent brim – you can get whatever you want from the internet.
Many people wear polo shirts or Tshirts and jeans most of the time, and only rarely dress up any further. About the only hats that really go with jeans are baseball/gimme caps and cowboy hats for men, with women having a few more choices. I do wear a straw hat in the summer to keep the sun out of my eyes and to keep my head a bit cooler, if I remember to. I don’t have a big selection, though, unless I want to order online and/or pay quite a bit of money for a hat.
Your missing out, if you haven’t worn a quality cap. I’ve worn Kangol caps for 20 years. I hace at least a dozen in use now.
The thing with caps is quality. Kangol is a British cap and it’s been around for 70 years.
I love my straw Ecuadorian hat, but only in the sun. It’s not something I wear all the time; then I’d just look like a stupid American tourist (who, I admit, I usually see strolling out in the streets in the sun). Other hats just don’t fit the attire for being in the sun, and baseball caps are for bald people and don’t protect the neck.
When home, I drive a Lincoln Continental (among other things). I always feel that I should be wearing a fedora or something that old people wear, because as far as I know, I’m the youngest Lincoln Continental owner ever (don’t worry, I know they don’t make 'em anymore; I’m thinking of upgrading to the Taurus SHO, unless we make the RS version of the new Focus for North America).
I didn’t see any good evidence that Kennedy hastened the demise of the hat.
My dad was very happy when Kennedy pushed them out of style.* It might’ve been the first step toward his becoming a Democrat.
The artist of the graphic novel Houdini, The Handcuff King was struck by how many photographs from the early 1900s show people wearing hats, jackets, and generally more formal clothing.
Check out this 1908 picture of a crowd listening to a speech by William Taft. Lots of hats.
I’m betting it’s for the same reason people don’t wear a suit & tie for dinner any more, or stroll down main street twirling a fancy walking stick that is clearly not being used to assist with walking.
This is more of an opinion but in this day and age clothing has become a simple necessity, worn only to comply with decency laws or to protect one’s self from the elements. Why wear more than is necessary? Those who continue to wear hats must see something beyond simple utility - the desire to dress up or emulate some hat-wearing personality. Those folks who still like to accessorize see hats as a means of expressing themselves via their fashion sense. But I’m guessing that the trend has been moving away from that since hat-wearing days of yore.
Then there is the cost, which can be significant for some of the nicer head wear. At the site linked above, basic caps appear to run from $35-$50. Most people will need a good reason to spend that kind of money on a cap.
And my full head of blonde hair looks nicer than any hat anyway. 
As soon as I looked at that picture I wondered if Brylcreem had anything to do with it. Nobody would want to mess up a hat by putting it on a greasy, slimy head.
Nor would they want to ruin their coif by mashing it down with a hat. As a little kid I spent much time preparing my hair to be seen in church, though my weapon of choice was Vitalis. No “greasy kid stuff” for me!
ETA: For that matter, I still use the stuff, though most mornings I just aim it in the right direction with a comb.
ISTM that Brylcreem was popular in the time when hats were de rigueur.
It’s great to see that fedoras and trilbys are coming back. I wonder if Mad Men has anything to do with this trend.
Bowlers look great on just the right man too. Khadaji, a hat maker told me that tucking folded paper towels into the inside band on each side works. It did the trick for me on one of my hats.
I wear everything from black berets with lots of white flowers to the hippest cowgirl hat since Hoppy had a girlfriend. Several cloches and countless berets. Old hats from the Twenties and Thirties – and even a mink pillbox (shades of Jackie).
I will be glad when women’s hats with veils come back.
