I am not sure what exactly you expect here. The guy is literally amongst the worst defensive 3B in baseball right now. Out of all of the players who played as many inning as he did at 3rd last year, his defensive zone rating was 4th worst. His outs above average was 4th worst. Slots 1-3 were held by people with 3 or 4 times as many innings in the field to make that many mistakes. His range was 5th worst in baseball.
Like we aren't talking about a below average 3b here. We are talking about literally one of the worst defenders in baseball. Even if he "gets better" he is still going to be awful over there. It's not like he is bad and has the tools that could make him better. With his tools, the gap between his ability and his ceiling isn't big enough to overcome his horribleness at 3rd. Even with his bat, because of his defense, he was barely a positive fWAR player. That's pretty impressive with a .760 OPS.