Straying off the reservation

I don't know about other gamers, but I personally find myself sticking to one particular genre of game (in my case, fantasy) nearly exclusively. Oh, I'll play the occasional Cthulhu adventure or some such, but rarely do I find myself playing, let alone running, a science fiction, supers, or historical game. I'm not sure why this is. It's not that I don't like things like movies or books set in those genres, it's just that I rarely game in them. Perhaps it's that I am usually the GM in my games and I'm used to running fantasy. Sometimes I think I'd like to stretch my wings a bit, so to speak, but there's also the risk of "gamer fatigue" from a group; where the players are just not interested in learning a new system or setting AGAIN. It's understandable, I'm as guilty of it as the next person, but I worry it sometimes pigeonholes a group and limits the potential for fun.