I would like to weigh in on this topic also, as it was a primary discussion point among my dad & I yesterday during the game.
I agree that Parker is not 100% and that is affecting his play. Moore is healthy & hungry and has played that way. To me, the biggest reason to play Moore ahead of Parker right now is that when Parker is in the game, the defense knows that he is no threat in the passing game, allowing them to play run first. Not only do the Steelers rarely look to get the ball to Parker with the pass, when they do, he shows very little ability to catch it or make something happen when he does catch it. Pittsburgh's greatest offensive success is when they have taken the underneath routes to Moore, Miller, & Ward THAT ALLOWS THEM TO MOVE THE CHAINS. This team needs to be able to string first downs together & get in a rhythm to be successful. I wish they could score more, but with this defense, the offense can contribute to the team's success by controlling the ball and eating clock. If they do that with the short passing game, so be it.
Right now, Moore is the better player to do that, because he is a threat out of the backfield & is running hard & smart.