And that absolutely can't have anything to do with increasingly terrible diets, studies in life longevity from healthy exercise, and the fact that the industry is almost entirely nutritional, which, while it goes hand in hand, has nothing to do with just working out?

Probably because people have recently figured out that they want to live longer and to do that you need to be healthier. There's nothing wrong with getting off your ass and shaking it every once in a while.