A post on here just now reminded me of buyer's remorse. I literally forgot that it was a thing, even though it was one of my own plateaus at one point. Reason being: I am closer to the opposite problem now.

There are probably a lot of factors contributing to WHY but as far as I can tell, this is what it all comes down to:

Defusing LMR:
Much has been written about this so I won't labour the point. Just do it. Make them WANT you, don't try to trick or coerce them into anything. You need FULL consent, not partial consent.

Proper Aftercare:
look, I'm really active in the bdsm scene and aftercare is a very hot topic. When you play with kink, it raises tremendous amounts of endorphines and dopamine (aka feel-good, lovey dovey brain chemicals) in the person being whipped - just like sex but more extreme. When the play ends, the chemicals drop and the girl is left feeling empty, cold, alone, depressed... all sorts of negative things, UNLESS her needs are taken care of properly. Those needs will vary from person to person but the #1 most common one is aftercare.

Aftercare is what you do immediately after a kink scene, or for you guys, after the close. Girls are rarely aware of their own needs because the neurochemical cycles are more subtle with straight vanilla sex but it is your job to learn about her and figure out what she needs. Here is a non-comprehensive list of what may or may not be needed.

1. Be present with her. Put your ego aside and think about nothing but her.
2. Cuddling. Just hold her.
3. Listen to her if she starts talking. Enjoy the silence if she doesn't.
4. Reassure her that she is good at valuable.
5. Get her water or snacks.

Sex can make her feel good but aftercare is meant to make her feel good about having sex. To make sure she doesn't feel disposable or too easy. It's about reversing buyer's remorse and making her want to come back for more.

One final point
If you fail to get past LMR, but you make *some* progress (making out and groping without actual sex) it doesn't hurt to do aftercare. She might already be feeling used and all that stuff... so don't get frustrated and storm off. Be there for her and acknowledge how awesome it was. That means you need to stop for a second and reason that just kissing someone really is awesome and worth enjoying.