Josh Smith still makes a considerable impact on the defensive end; he's better than Hayward.
Additionally, he's being asked to play a role for significant stretches that he's perpetually gotten worse at (being a 3, in layman's terms) and is a particularly moody player being asked to do things he doesn't do well on a bad and increasingly dysfunctional team. But as a 4 on a winner, I think he's still there.
Hayward's just not that talented and does no single thing at a high-level. I didn't know the market for jack-of-all-trades-master-of-none was the max.