When Moyes arrived he had the choice of leaving the first team on auto-pilot with Meulensteen and Phelan until he got used to the demands of the job and the personalities of the players. He chose not to. In management, including any kind of people management, you live or die by that kind of decision.
By deciding to dismantle the support system there was no one there to stop him making naive mistakes - like taking the team for a walk on the beach on the pre-season tour (and getting them stuck in a crowd, waiting for police/security to rescue them). It's a trivial thing, it shouldn't matter, but it does because players are humans too. They'd have laughed about it at the time but as more serious differences from the old regime - like more running Vs more ball work - started to appear, it turns into "what does he know about managing us?"
Should the players have been model, self-motivated pros, keeping silent about their misgivings, even to each other? Sure, but that's not how people are. If they're not happy they grumble, the moan, they bicker. They don't give their best performance because their heads aren't in the right place.
A few years back, when Redknapp took over from the (sacked) Ramos at Spurs I don't remember SAF being very sympathetic to Ramos. Instead he made the observation that the Spurs players had gone into training smiling, and how that was good, because the training ground has to be a happy place. I don't think United's training ground has been a happy place this year.
I'm not too impressed about the Monday leak of the Tuesday sacking, I think that was unprofessional and discourteous. The sacking itself, I was relieved when it happened. I'm actually looking forward to our remaining matches and excited about next season. I bet the players are too.