It is interesting what is coming out now. Most of it is probably true, who knows, in any case, none of it is terribly surprising. I have to speculate some, and read between the lines some, like all of us, but a couple of things seem to be getting clearer or more in focus.
First, the shadow of Udoka was there all season. The players liked Udoka and did not fully understand why he was fired. This made it harder for the players to buy in to what Joe was trying to do. I think the offense did need another level of sophistication or nuance. More secondary scheme or movement in addition to the primary, often pick and roll scheme. In my opinion, the offense was too predictable. Not sure why that would be mutually exclusive to focusing on defense too. The reports seem to be implying that the players resisted the work on offense, that it was taking away from the defense in some way. I know playing White over RWill was part of it, but I am not sure why this had to be a problem. It probably wouldn't have been if not for the "Udoka shadow".
As to the assistants, first, the guy they came here to "coach for" was gone, suddenly and based on not fully revealed issues. Then, many of them were passed over (or would have felt they were passed over) when they picked Mazzulla. Fair or not, I can understand how these other assistants must have felt. Now they are leaving, some to new opportunities, some back to Udoka. The assistants appear to have not bought into Mazzulla any more than the players.