Equal number of partners does not mean equal levels of emotional investment before and after sex.
How many post do you see on this forum from men saying that a woman stopped texting/ grew distant after sex. Compare those to the number of posts you see from women.
I'll narrate briefly my experience after I slept with the guy who initiated stuff. After we slept together it was as if a rough snapshot of him had been imprinted on my mind..if I saw some one who had a similar body type I had a heightened awareness of them and def the adrenaline levels went up. I was invested in a physical/ hormonal way. A reaction that is primitive and has nothing to do with cerebral. The sort of physical reaction he probably experienced during the pursuing phase, but that wore off shortly after.
I used to get texts etc from him or talk to him. My conscious mind often thought of these communications as being lacking in color, imagination, flair. I compared those to what fun colleague of mine at work might send..or my husband for that matter. I was well aware that for me at our conscious interaction was at best pretty average, and I wondered whether I could not get as excited about intelligent, fun communications from other people. But communications from him again evoked a physical reaction.
In this way he stayed embedded in my mind, whether he was there or not. If he wasn't some one roughly like him sufficed to keep the snapshot alive.
This is primitive biology. It affects our behavior..that's why so many of us are at war with ourselves..women more so. Our emotions telling us that some one is essential for our existence while our head tells us we don't like them that much. This is because millions of years ago these guys genes would be in our kids...and we could have much fewer kids than men. So it was important that they stay invested in us and we them.
Many people might disagree but I think the biological differences between sexes are obvious and bear out in day to day reality.