It's not that the coaches are thinking, "Man, we really need a guy that can't move back there." It's that they are looking for a guy that is a passer first. If they can get a guy that they think can hit all the throws and read all the defenses and then is a running threat as well, of course they'll take that guy. But more likely they will find a guy that can move a little bit and do the things they require of a QB. That's why they took a guy like Morris, not because he's just bad enough at running that Michigan should bring him on board, but because they believe he can do the things they require from the position and he isn't a terrible athlete on top of it.
this may be of some local interest