Sports titles, such as Madden, due to their attempt to simulate a sport, and attempt to add new features and balance them with playability. With First Person Shooters, there isn't any sort of simulation involved here. So, I don't see why there would be a need for what you have with sports titles, where they are also new rosters.
But, maybe there are things left that need to be done. On that note, I would have to ask, what does Halo, Call of Duty, Battlefield, or other FPS titles I mention need to have done with them, and new features they need added? What is needed to be added that couldn't be addressed with either an expansion pack or a patch?
So, why aren't FPS now where music games or driving games are? What other work is left for them to improve upon?
