Okay, let's take a step back and look at things from 3rd person POV.
Men and women have one thing in common, we're both the same animal; human. We have the same desires, the same needs, and besides not being able to both produce eggs and sperm, we have the same things to offer one an other.
All else constant, there should be no differences. But society says there are; so there are.
During childhood development, as a male, you're told that unless you have sex with hoards of female humans, you're a loser. That the thing you hate the most is commitment and relationships, and what is most valuable to you is out-of-this-world, amazing and frequent sex with the hottest supermodels that ever walked on the face of the earth. As a female, you're told that if you have sex with hoards of male humans, you're a sIut. That the thing you hate most is being alone, and that if you are labeled a sIut, you will be alone. Ironically, if you're labeled a prude or virgin you'll also be alone, and if you're labeled a tease or whore, you'll definitely be alone. But what is most valuable to you is commitment, stability, security, and a happy marriage and family. That unless you're the perfect mom and wife, you're a loser.
So even though we're both human, these socially created and enforced roles based on our sex, shape our behavior, thinking, and most importantly; beliefs.
If you're a man, you might believe that women are asexual, have almost no desire for sex, or only pretend to desire sex so they don't get ignored and until they eventually get someone to marry them in which point they will no longer have to pretend anymore.
If you're a woman, you might believe that men are emotionless, have almost no desire for a relationship or love, or only pretend to want those things so they can have sex, and once they get what they want, they stop acting and move on to someone else.
Irreguardless if true or not, for as long as these are the core beliefs of men & women, these beliefs will cause them to behave much like two parties negotiating in a board-room.
Men will feel that they have (love, commitment, money, marriage, a relationship, emotion) as their bargaining chips, that everything else they can offer is not of value to women. Women will feel that they have (sex) as their only bargaining chip, that everything else they can offer is not of value to men.
And so, the negotiations begin.
But as men discover, women want sex too. And money and emotion just won't cut it.
Similarly, women discover, men want emotion (and sometimes money) too. And sex just won't cut it.
So why do SOME women do it? For the same reason SOME men take girls shopping, get them stuff, do things for them, listen to their problems, tolerate playing hard-to-get and games, go through the motions of dating, etc; because they believe she'll appreciate getting what she wants, and will make her feel for him, what he feels for her.
That's all there is to it..