I'm assuming they mustn't be very effective. I'm saying this from the perspective of a dancer, a dance belt would be covering up some of what these guys are still showing
A thin lycra base layer isn't going to hide much more than the thin lycra layer over it. Your mostly just trying to keep everything tucked in out of the way and not bouncing around. Not trying to be turned into a ken doll. And having your stuff crushed into no existence would be kind of annoying. Why should we be ashamed to have a dick or to have balls ?