That is an excellent question.
Possible answers:
- Nintendo is content to allow Sports/Fit/Kart drive sales and holding off on releasing other games until sales show some sign of softening.
- Nintendo never releasing games until they feel they are finished and they don't have any ready for Q1 (except D:DoC for NA ... >_
- Nintendo is focusing a lot of development elsewhere (DS2??)
- Nintendo is holding back Wii games until Wii Sports Resorts and WM+ comes out (cause they all use it?) and it's not ready
- Nintendo staff are too busy partying with all the billions they are making they are either - too busy partying, too drunk or too hungover to work on games
- Some combination thereof