I've quit games for various reasons, but most people here have hit the reasons why. I will tell one story though, leaving out names.
I played a game at the request of a friend, and I thought it would be fun. Instead it was a series of cliques where finding RP was difficult and sometimes just flat out annoying. I finally did find some RP there with a group and we had a lot of fun, and people seemed to get upset at that. We were having a scene one evening, and halfway through it we were paged by staff to tell us that what we were doing was not in line with the MU*'s story, and we would have to disband our RP. What was the error? We were having a party, late at night, with boys and girls with no parents home. We were not being inappropriate, in fact, all we were doing was eating pizza.
I don't mind being tutted or told not to do something, when it makes sense, but teenagers hanging out at a house where the parents were at work, eating pizza? That doesn't happen? It's not allowed to? It was just weird, and after that I felt like everything we were doing was being watched, in a really creepy way. Left shortly after.