Because they didnt sell with with the cube and wanted to do something new. Heck look at all the games that were praised for being new despite the fact they were garabge! (Sonic and the rings is a prime example). They certainly do make games for what they want to do.... its just a damn shame we are stuck with it for 5 years + at a time. Making games meant to "showcase what motion controls can do!" 5 years after its launch is weird....
Just like Star fox zero showing us what the game pad can really do!... as the shoot the Wii U behind the barn.