In my opinion, and I have nothing to back this up, pitchers get hit in the head more often than the face. While you want to catch the ball, you look away if your face is about to be crushed, more often than not. You watch the video of Fister, and he clearly looks away from the ball.
You know if a pitcher is killed, they're going to put helmets on pitchers. Just like they did base coaches. So why not now and prevent it?