I think it's because at one point in American culture, having a big booty was seen as fat and it didn't matter how well in shape the woman was.
With that said, White American woman did become obsessed with having a bigger butt. That's why at one point, you had so many of them doing those squats and lunges. It's the same thing with big lips: they stayed getting injections for their lips nonstop at one point.
Anyway, I think the big booty trend has ran its coursed. Mainly because of all the fake booty injections and so many chicks have booties so large that they look unnatural and cartoon like. It seems nowadays, people have really gotten into fit and healthy bodies and that's including Black men. I'm seeing more Black men prefer a fit and toned healthy sister over a big booty Judy who can hit it low while doing a split. Of course, to each its own, but still.
Also, some of y'all are fukking weirdos who need counseling.