I think there's more to it than that. You mentioned that they don't just go there, but that they are "rotting" there. I think that things are getting more difficult for men, normies included.
Go take a look at the 16-22 age range. Foids are getting ahead of boys, or rather, society is letting boys behind. If you are a 16-22 year old foid in high school or university and you have energy and you want to do something with your time, there are countless opportunities open to you, as a fully socially integrated person: part-time jobs, tutoring, hustles, and anything that you could find to spend your energy on, either from friends or by yourself, because of how easily foids are accepted everywhere. If you are a 16-22 year old man, full of energy and desire to spend it and build something, there are good odds that you won't be accepted anywhere. You won't find a place where you can spend this energy and your desire to be productive and do something with your life, other than... the gym.
That's maybe why they "rot" there. While chads and foids get to build their lives, average and below men can at most get to build muscles.
In other words, gym is getting on par with videogames as the go-to time waster for people who have nothing better to do. It satisfies the same needs, grinding for levels in a game is not much different from grinding for gains in the gym. They are both surrogates of the real things that we'd want to get.