I think it has to do with the fact that Nintendo games tend to have very long legs. Unlike cross platform games many Nintendo games actually don't sell the majority of thier units in the first month following release. If Nintendo were to release a second Mario Kart game on a platform the first Mario Kart game would probably stop selling alltogether and the legs would be replaced by the new mario game. So yeah they sell maybe 4 Million units to the same people who own the first Mario Kart game but after that they just be selling the new mario kart game instead of the the old mario kart game to a late adopter of the system.
A game like Mario 3d makes sense to release a sequel as well as something like Metroid Prime where a larger percentage of the buyers are core gamers. But for 2d Mario and Mario Kart I don't think there would be a huge benifit sales wise and Nintendo is better off creating an expasion pack like they are doing with the new Luigi expansion in New Super Mario Bros U because it won't have any negative affect on the legs of the main game. They would also be better of creating a game with a different flavor such as a Mario RPG which caters to a different audience and will have it's own legs.
Am I wrong here?
