That was also his first game after missing five with the finger injury, and he's going to be in a brace for the rest of the regular season probably.
Listen, he's old and injury-prone and hasn't been able to hit the ceiling of what they need from him in terms of carrying the team when Joel can't play, let alone the superstar ceiling but nobody expected that. The season is a bust and the contract might be too. But he's still the #3 the Sixers wanted (and the idea was not for Joel to be out this much, and also that Joel could carry the team when George can't play).