I've seen a few straight guys advertise but usually they look like farmer joe's. There is the argument that ladies can get sex whenever they want but it's the quality of sex and let's be honest, an ugly lady no matter how much she does herself up isn't going to pick up a really good looking guy. It doesn't work like that, an ugly guy can get a a good looking lady but generally it doesn't work the other way around, unless she's loaded of coarse.
But that said women don't use this site and if they did most would have a moral problem with it.