Alva Noë makes a game attempt:
Cartoons don't give us glimpses of worlds, they give us worlds to play in and toys to play with. Live-action movies, in contrast, don't give us opportunities to play; they give us access to hidden worlds. Here, then, is what I propose: the uncanny valley yawns not when animators fall short in their rendering of the human body — even if in fact they do — but rather when they get confused about what kinds of stories they are telling: Are they inviting audiences to play, or giving them an opportunity to watch? In this confusion, the story dies, and with it, the light in the eyes of the characters.
It's also a decent way to explain what's wrong with Mitt.