I have the same habit. I don't use the victory conditions but if it gets to the point where I'm so far ahead of the other empires that I know I'm going to win, it gets boring and I start a new game. Or sometimes I just start a new game anyway just because I feel like using a different racial tech or whatever. Or if I don't play for a few days, I don't feel like continuing where I left off so I start a new game. I've only actually finiahed a few games ever.
