I am aware this might not be the experience of every couple but the many couple I have interacted with, the story is pretty much the same: the wife losing interest in sex once she gets married to the man and especially once children start coming. For certain couples it isn't as obvious as that, the wife simply approaches sex as a mechanical function that she needs to get over with and perhaps do something else. Why do you think this is so? Can one say it's because once married the woman feels socially secured and doesn't need to put in any effort to win the man? Or does it have anything to do with changing biology?