I've never been in a serious band setting for very long and the ones I have been in we all went in knowing it wasnt going to last for various reasons anyways. I have played with a ton of people however and its pretty easy to see why bands break up over time. Lets face it, a lot of times you just dont click with others. Band mates are a lot more intimate than coworkers and the such. Not only do you spend a lot of time together, but you also inherit their personalities, habits, feelings, moods, etc, while working with them and the output depends on making it all work in a musical context. As a drummer, you have to be able to lock in with the bass player or its a huge fail. I've played with a bunch of people in which we wanted to kill each other after playing. The music got played, but there was no way I was going to hang out with them afterwards. When relationships become that toxic, people tend to distance themselves from each other.