You are talking about his ability, whilst overlooking his attitude.
It's not his ability that is currently in question (well, mostly...) It's the persistent rumors that he is poison in the dressing room and didn't give a crap about training or the team, until this pre-season, when he suddenly seems to have realised that the wheels are coming off his gravy train.
He's not been shut out because of posts on social media ffs, he has been shut out because last season his attitude visibly stank and he wasn't very good at his job.
If he had just joined another team and had lost weight and was ready to go then fair enough - I can see another teams fan's saying 'let's give him a clean slate and hope he can turn it around', but there's just too much baggage surrounding him, and my guess is that RDM doesn't want his attitude influencing his new team, and I agree with that decision 100%.