The brain of men releases masses of endorphins and other chemicals that make them drowsy and in some cases even cry or feel guilty (very odd I know) and the whole mix of chemicals tells a man that sleeping with a woman now would be akin to sleeping with their mother. So not only do they want nothing to do with you but they feel elated and slightly guilty and sleepy. It's obvious why this is, your semen is about as reproductively capable of insemination after a squirt as tap water. It needs time to replenish the liquid so that the sperm are better able to fight for freedom for muldavia and get women up the duff. It's simply evolution. Mind you that doesn't save you from being ostracised when you roll over and pass out, and all she wants to do is spoon. Put in animal terms, its I've had it now go off and fertilise my child, and don't come back for a while so if we do it again I can baby you up.
Obviously your semen has no idea whether it and it's happy campers are going into the womb or your duodenum as well or going to be splattered against a rubber wall of toxic death. Nor does your brain discriminate either.