BI needs to have the ball in his hands in the 4th simply because he is the focal point of defenses, and his point forward skills make it easy for him to find the open man. Watching the last 4-5 games, it seems like all the elite teams game plan around him, sending extra defenders (and sometimes prematurely) to contest him in the paint. This means someone is always going to be open. For example, here's the sequence where two guys shadowing BI led to an easy oop for Kuz. It just makes Kuz's job that much easier. He also generated good looks for Hart last game. Stuff like this won't show up on the box score but it sure as hell is the reason the coaching staff puts unlimited trust in BI.