1st off, he was a rookie. It takes several years to put it all together in this league.
Secondly - He was never the 1-3 option in the offense. There were times he didn't even touch the ball, or was not called to go down low.
Next - Anyone who's had a pretty good ankle injury will tell you that this thing goes on, and even when it feels fine, it's not. It's an injury that needs to be 100% & there's no time for 100% in the NBA.
Give him a couple more years, and watch what happens with this team. He just doesn't care about stats, his number one concern is winning and it reflects by his willingness to do anything on the court that's needed to win.