Not just the structure of society but biology.

If a women risks getting pregnant every time she has sex then she always going to be more picky than a guy in any situation.

I think women's requirements in a sexual partner actually goes up for causal sex while men's hits rock bottom. They definitely go for more macho men in one night standd. That means less macho guys have more chance of finding a long term partner than screwing around. But they see the guys who women screw around with and think they have no chance.