I have a theory about this.
DITB (Dick in the Brain). The thought processes of men are often dicktated before sex by their smaller brain (the dick). When this dick gets in the brain we lose control of our senses and try to find the fastest way to release sperm from our testicles. It can be seen in bars, SCs, MPs and even on dates. We can be seen spending extravagant amounts of money, saying the dumbest things and acting like fools while we have DITB. The proof of this theory is evident just after the release. Just after we cum, we are compelled to say something stupid to the one we are with. (just listen to yourself the next time you are at an MP) Once the sperm has left the body, the normal brain takes over. This is why so many of us wonder why we spend so much money on this hobby just after the session and not before. Normal brain is responsible for sleep, work, food and finances. DITB returns frequently and when it does, it makes you do things like pay for sex.
Women on the other hand have PITB (Pussy In The Brain). Due to the different physiology of women, the Pussy lies dorment until they have sexual relations with a man. The Pussy however can distinguish between paid sex and free sex. The pussy can ignore paid sex easily (more evolved?) But free sex is where it comes into play. Once they give themselves to a man, PITB takes over and starts to put crazy ideas into their heads. This is why so many women like to cuddle, have the man sleep over, etc.... Sometimes this can be worse than DITB because it can plague the woman for a lengthy period after sex. Questions like is he happy? Will he call me again? Why is he not calling me? How does this affect our relationship? How does he think of me now? How long is this relation going to last? Why is he not answering the phone? Why is he not calling me back?
If women could pay money to have men act in an ideal manner after the sex, women would spend just as much money as men.
I could be wrong, but I think it's a responsibility of man to try to understand the differences between men and women. Unfortunately, it is also the destiny of man to fail at this task.
Even more unfortunate is the fact that if we do not try to understand this, the woman will be pissed off and we will not get sex anymore and DITB will run rampant and we will end up paying more money for sex.