Because men pursue and women are pursued. This is the nature of human sexuality.
A virgin girl who gets approached by men all the time and rejects them, but gives herself to a man that is going to make that man feel very special.
A "player" who chooses to settle down with a woman is going to make that woman feel very special, because whilst he could be out banging loads of girls, he saw something in her that made him want something more.
It's all about sexual dimorphism and balance. Men and women are different and society works better if those differences are recognised.