Viva Pinata wasn't a system seller though. Goldeneye was a system seller. Banjo Kazooie was a system seller. And so on. Not to mention even quality wise while Viva Pinata is good...its just that GOOD not GREAT not AMAZING, but GOOD. And that's Rare's problem, they don't make games that will make people buy the console or games that even really stand out that much from the competition.
Kinect Sports sold because it was a Wii Sports clone, that's pretty much it. The game itself isn't really that good. Even then so that's two games over the past...near 13 years. Nintendo most likely used the money to sell Rare to further build their in house and gain talent (like Retro). I mean really the only thing that makes Rare stand out today is that they are seen as a shadow of their former selves.