Why didn't he throw over then? In short, an abundance of caution. There were zero outs, he's already moving towards first, he's left handed so he has to wheel around completely one way or another, basically the same reason every 10 year old is trained to go to 1st in that situation. He was almost stumbling towards 1st base, so the throw to 3rd would not have been near as easy as Schilling was making it sounds.