So in other words you have high metabolism. A lot of other people do not, so it's just a bit arrogant to say exercise is 'a fad' just because of your anecdotal experience.
I think it's more than a fad, it's more like a cult, or a cultural ritual.
I don't watch much TV or consume much advertising, but on the occasions I do, I'm blown away by how heavy the marketing emphasis is on being fit, one way or another. Marketing thrives on people's self-perceived inadequacies, because it creates a very base need for products.
Not being plugged into the culture, I feel its pressure all the more. It may be confirmation bias, but I perceive the downvote as a form of peer punishment too.
The downvotes are because you are insulting a part of many peoples lives which you pretty much claim to know very little about. For one, I want bother linking because any simple search will yield the results, exercise is, not surprisingly, the root of many physical and mental health benefits. I've read numerous stories here on HN showing how it can help lift people out of depression, and exercise is important to many professions and hobbies.
But aside from the direct benefits, does marketing show healthy and fit people? Yes it does, but I'd go out on a limb and say that even without that, people of the opposite sex will find healthy physical features attractive, so you're always going to have people do it for that reason as well. It's not the most noble motive (however you define that), but you shouldn't ignore the other very honest reasons for exercise just because you hate the stereotypical gym jock.
IMO you're coming at it from the wrong angle. i don't even own a tv at all. yet i compete in bodybuilding and go to the gym every day because i love it.
just because your idea of what is fun doesn't mesh with someone elses, doesn't mean it's stupid.
additionally, your n=1 example of eating whatever you want and not getting fat holds little statistical significant. when the average person consumes more calories and doesn't make up that increase in caloric intake with exercise, they will gain weight over time.
