It was a carrot and stick thing for me.
Carrot: Its a real puzzle, I enjoy the intellectual challenge, this is the main reason. The project is interesting, I like to do application-oriented research. I get to read cutting-edge stuff, and I get to do tons of programming as well, which I like. I got a bit of extra funding from an industrial sponsor so it is about the same money as I got in my job, but unfortunately without the generous pension. I get lots of support from my supervisor. The university is not that far away from me, so I did not have to move: I own a house and have school age children.
Stick: My job was boring, I was working as a database administrator (really a sort of junior database developer). It had no real prospects for advancement, improvement or training. It was not particularly well paid, either. The I.T. department were not respected within the organisation and decisions were made without consulting those who know about the issues.