Exactly. Why bring him in and risk screwing up this. Pro athletes are extremely competietive so he's not just going to come in and take the proverbial backseat w/o a fight.
As for his behavior, he was a notorious partier w/ some fights at clubs to his credit. I also remember some very douchy photos of him at clubs w/ his shirt off. He also was known as a guy who was last in and first out.
Also, he is a one-read type of QB that doesn't go through all of his progressions before he takes off and runs.
Lastly, he WANTS to start. Sure, he'll probably say all the right things to get through the door, but after he's in he's going for the starting gig.