I definitely think you're right about the "2k fatigue" theory. I've thoroughly enjoyed 2k games, all the way back to the original you mentioned on Dreamcast, but at this point I just want badly to play something else, without sacrificing too much in terms of game quality. That being said, 2k has plenty of faults as well, some of which have not been addressed for years now.
As I mentioned, the animations in 2k look great, but you lose that ultra precise feel to the controls when guys are constantly getting sucked into collision animations, etc. Their servers have been embarrassing as well, and don't get me started on some of the completely broken functions in the game, like the end of game highlights not working, or those days when the 'NBA Today' is a day or two behind schedule.
These may seem like small gripes, but when they never seem to be addressed, it compounds the fatigue of playing the game for so many years. I'll still give 2k a thorough opportunity to win me over again this year, I'm just really hoping that Live somehow magically turns out to be solid.