I'd say defense is moving him from shooting by playing him tight and "funneling" for him to drive.
its the NBA and defense give and take. They try to get teams to do the what they are not best at and sometimes it executes or not. Kat going to the hoop is not a bad thing. This is his first year here and for many of us our first real look at him. Thus if he drives more he wants more contact and teams obviously want him whining about it. Takes him out of the game on defense if on transition.
Also, does his finger injury have anything to do with it?
We give teams the 3 more because we don't have rim protector back there. With Mitch, that could change some. Towns/Rudy thing I sure was studied by Thibs. Is this the only reason? Of course not. But if we defend the 3 better what other issues arise?