reason #1: boyfriend
- it's very hard to maintain a relationship if your job is to fuck other people, so many girls quit because they met a guy they like
other reasons:
- you're getting tired of it (porn is not something you can do forever and while it might be totally fun in the beginning, after a while it just gets to you. physically and mentally)
- you just want to move on with your life and prove to yourself that you have other qualities than just spreading your legs and while the money might be still good, you really need something else to do
- it's hard to keep making money with porn over a long period of time, usually a girl is only in demand a few month or so
- rare cases: you made all the money you could and now you move on
- you start getting recognized on the street, everybody knows what you do, old friends stop talking to you, your family wants nothing to do with you and your whole social life just falls apart. that's when you realize you need to quit
- you are fucked up on drugs and not even able to succeed in porn because you are too unreliable for even porn producers to deal with you so you just disappear because nobody wants to hire you
just a few reasons. there are probably more, I would say 95% it's a boyfriend even if officially other reasons are quoted (different job, moving on etc)