I dunno. A racer tends to last a lot longer than an FPS. FPS's (and to be honest, there's only a handful of series that consistently sell extremely well) have short campaigns and addictive multi-player. The main story is over pretty quick so it's time to move on OR the multi-player is fun but the next big thing is always coming out. Graphics, features, maps, weapons--with FPS's, they're always evolving.
With a racer, the single player can take months to perfect. The graphics of an early racing game are actually comparable to a new racing game. The multi-player is "you race your friends to the finish line". We've been there. We've done that. I used to LOVE racing games. Now, I'm content to play Burnout Revenge (which is about four years old) when I need my racing fix. I don't feel like I'm missing out on too much.
Keep in mind, this is just opinion.
