Kinect, even with its sales numbers, is not a large segment of gamers. Not larger than the Wii owners, not larger than the iOS market.
Why would any developer develop exclusively for Kinect? And what game is going to do well that is built to work well on Kinect but doesn't require it? Either the Kinect part will make the controller part hard to work with OR the controller part will make the Kinect seem pointless.
Move works better because it adds to rather than takes from the games that support it. It'll be interesting to see how many people who are buying Kinect+Dance Central wind up buying any more games this time next year for Kinect.