Most teams, if they are in a situation where they "really need a bucket" will iso their best player. If Cleveland "really needs a bucket" Lebron is getting the ball to get that bucket. And it makes sense to do, IMO. And apparently, in the opinion of many coaches as well. If I need a basket bad, I want to limit the number of things that can go wrong, and simplify the situation. Diagraming up some random play generally will involve other moving parts, pieces, and others touching the ball. Opening up room for error. If the ball is in Roy's hands, or Kobe's, Lebron's, Carmello's, etc., the things that can go wrong are minimized. The different things to do to free up Roy, what if that doesn't work? What if that very good man defender denies him the ball? Then, when you really need a bucket, you're relying on someone other than your best player to get it for you.