Like tobacco companies and nicotine, the food industry has learned how to spike processed foods with a combination of salt, sugar, and fat that are addicting and most people don't even realize that it has happened.  Dr. Kessler wrote a book about it.  As others have suggested, sitting a desk all day doesn't help but the real enemy is highly processed foods.
Obviously, our standards for what a desirable body should look like have changed dramatically over the last 30 years.  Action figures used to look like real people; now they all look like roided bodybuilders.  The film Bigger Faster Stronger had a segment on this evolution...