Why aren't women more promiscuous?

I am serious about this question, despite its somewhat sexual context.

We are supposed to believe that much of our phisiology and behaviour were developed over thousands (or millions) of years. If we had females that were promiscuous and females who were not, why didn’t the promiscuous ones have more sex acts, and more offspring, providing ever more promiscuous females?

I understand the argument that women choose their mates for family stability and childrearing, I just find it hard to believe that this factor alone could outweigh the positive feedforward of promiscuity.