Bulls had goals of making the playoffs and right now they're in danger of not even making the play in tournament. Zach has already made it obvious that he's ready to start winning so the benching makes sense. Bulls had to eventually pick a path and it looks like they have now.
Coby is at his best on the bench and can still be developed from there. As for Wendell dude is mentally weak and lacks confidence to the point where he can't do anything right. Not looking good for him lately. If he doesn't change his mentality he's gonna be outta the league soon.