Because it was time. My guess is Butch obviously hates that he had to finally pull the redshirt, but I bet he is excited tonight. Remember, there is one qb on the roster that he picked himself, and it's Dobbs. He can't preach family and come in and bench an upperclassman leader in Worley, who is liked and respected, and put the trust of a new program in a true freshman right off the bat. I think Butch thinks ahead a lot, and that would've possibly divided an already fragile locker room.
Now, his guy is in there, and there is really no debate, imo, as to who has the reigns now. I think the thumb takes the pressure off of him.