Who? the men or the women?
Just like with gay porn. A lot of these different niches/fetishes/body types are segmented out. If you want milfs, you go to the milf website. If you want BBW, you go there. Trans porn, you go to the trans site. Granny porn, you go there.
That's how it's always been.

As far as male bodies go, yes there is more "diversity" but that's because the standards are much lower. You just need to have good dick and at least some decent stroke game to make it. Being fit or handsome are not requirements. (hell these days gay porn standards are just as non-existent really lol smh)
Consumers of straight porn don't care what the man looks like, they are focused on the women. (The exception maybe being cuck porn where the cuckold's appearance does factor in somewhat) The women are overwhelmingly conventionally attractive and young. Just like gay porn has mostly conventionally attractive guys, niche websites notwithstanding