It adds to the degradation/humiliation aspect, you have these incredibly beautiful girls, perfect, prim and proper in every way shape or form getting railed by some of the nastiest and ugliest motherfuckers you can ever imagine which, under normal circumstances would've never had the tiniest chance to lay their grubby hands on these ladies but by some cruel twist of fate they do get that chance and some people find that to be a major turn on, some don't.