In my experience, half the time this is due to the guy(s) the woman was previously with being incompetent at the overall process (which is far more complicated than the mere mechanical act of sex). From the standpoint of the woman, this seems to be a crapshoot; some guys are figured things out quick, others didn't. Obviously, most of these issues can be worked out in a decent long-term relationship (married or otherwise). That said, there do seem to be a small group of women who have mental/psychological issues that are largely independent of anything involving the man.
I have met a couple <30 virgins, but they are very rare (no thanks to me in my younger years).
I went to the store this afternoon and on one of the magazine covers was an article entitled, How To Tell If He Is Justing Using You For Sex.
If you live in an insane asylum, insanity becomes accepted by even those who are not insane. To me Tip #1 for the girls is, IF the guy is bedding you and you do not have a ring on your finger, it is likely that you are serving the function of an inflatible doll. You are just warmer. Guys treat girls that they are interested in with a slightly different manner than they do the girls with whom they have no interest.