Okay, I'll get straight to the point about why it works like this. Evolution has gone on for millions and millions of years, and females are, in more or less all advanced species, very selective about men. The reason why is because a female will have to bear the child of a man for many months, while a man could easily have a huge harem of females. Well, maybe not easily, but a male having sex with a female only gives her trouble. The guy can just move on to the next female.

Women, as a stereotype, care about a man who can support the family, protect them and soforth. Males just want a chance to pass their genes along, and the better the female looks, the better will the chances be of having a good, fit child.

Simple Darwinian evolutionary terms, but it really works that way, far more than you think.