I think Mickey is such a founding part of Disney, but there never was a real story that was obvious for a ride. Sorcerer's Apprentice is probably the closest actual Mickey movie that would have made for a dark ride or thrill ride, but Sorcerer Mickey is used in so many areas of the Parks that it would have felt restricting to tie it to just another ride in MK. I think almost from the beginning Mickey was meta Disney World, uggh that hurt to type but it gets the idea across pretty well, instead of just a character. And I think his ubiquitous nature in WDW, which is kind of unique to him, resisted any simple attraction. So I don't think there was really a desire to, maybe, pigeon hole? Mickey into a ride unless the perfect opportunity came around.
With DHS going through a rebrand, and the Sorcerer's Hat coming down, and the centerpiece of the Chinese Theater coming open, I think there was that perfect opportunity to build Mickey a showcase without pigeonholing him into, say, a corner of MK. The prestige of the location and the lack of really anything else "Mickey" in DHS made for a really good marriage for the first time in the Parks. Mickey gets the place of honor, the ride at the center of it all, and that's kind of what he deserves. Short of Spaceship Earth, where a Mickey ride would feel out of place, there wasn't a place grand enough for him before.
Kind of a hash of a post, as I reread it, but it's a hard concept for me to explain. He's just too big, too important, for just a ride. It needs to be THE RIDE at the center of a Park. Only DHS can give him that position.
