Disney has minds that are smart enough to develop ways to entertain and excite guests beyond popping in characters. The problem, in their eyes, is that it takes more time, effort, and money to do that. Except for unusual cases, adding Disney characters to works that are not already character based acts as a band-aid for a larger wound -- and, at that, a band-aid that further damages the Theme of the Theme Park. If Innoventions isn't exciting people, it's probably because Innoventions isn't exciting.
I'm all for opening kids (and adults) to the exciting worlds of science. Tagging on a new character only goes so far towards doing that.