I guess that they wanted to maximize the reaction of the feel-good moment. They noticed that a win at Fastlane and a loss at Wrestlemania wouldn't be as good, in terms of crowd reaction.
As for Vince saying he wanted KO because he's more "box office" and still adding a third man: it's supposed to fuck with Kofi, he's doing that as a power trip and to spite him. It's not really complex at all, guys.
Plus, the addition of Ali to the match was a twofer, because I imagine a straight KO vs Bryan match would not only die a horrible death, but KO losing on his first big match back is unnecessary. Ali can cope with a loss, and his bumping is obviously going to get a reaction from people.