They didn't start any KH project on a Sony console. I'm not sure where people are getting this idea, but the only game in development right now is the KH spinoff and its platform isn't confirmed.
But one reason KH3 would be on Wii is because Disney said so. No, really. They've been pressuring SE to put KH on a Nintendo console since KH2. Disney has the best relationship with Nintendo and they want badly to get in on the family market, since that's who Disney movies appeal to anyway. SE really doesn't have a case against putting it on Wii now since it took the place of PS2 this gen.
It may be the spinoff, it may be KH3, but either way, one of the upcoming KH projects is definitely going to be on a Nintendo platform.
Tag - "No trolling on my watch!"
