I think it's a matter of expectations. People think he should be jokic/embiid caliber, but he's not that. He's a few tiers below that as an average starting C. Compare him to guys like Poeltl/Valanciunas/Capela/Wendell Carter jr/ Zubac/etc etc. All of the guys I mentioned are inconsistent with mostly average play and the sporadic instances of greatness. They all have issues with motivation at times. But Nurk's salary is commensurate to that production.
His finishing issues are at the forefront so that's all most people see, but he more than makes for that with his defense. He's averaging a nearly his career high in rebounds, and rebound %. He also protects the rim at a close to elite level even while not blocking shots. And his passing/shooting have improved quite a bit. I don't think people realize how much Chauncey asks of him on the defensive end of the floor for us. But you hardly ever see anyone acknowledge that; rather, they'd just ship him out because he misses layups.
He's got weaknesses obviously, but the way people trash him here is unwarranted. And I think trading him for a guy like Turner would be a very lateral move in terms of overall impact (hell I think Nurk is better for us than Turner would be).