Square couldnt even get Sora for Dissidia 012, even though they explicitly said they wanted him.
Dissidia was originally going to be about Disney characters (and KH characters), but Nomura didn't feel comfortable with having Disney characters fight, so they made it about Final Fantasy instead.
^ This is true. I hate when people think that it was Disney who said that Sora shouldn't be in. It was Tetsuya Nomura