I think Bill Walker and, to some extent, Nate are evidence of the messed up chemistry on this team and how Doc had handled it in almost completely the wrong way. It's pretty clear that there's a conflict between the vets and the younger players over how the team should play and Doc has let it fester all season.
There were plenty of games where the vets were either banged up or giving crap effort and Walker, no matter how awful his defense, should have gotten some minutes. Likewise, it seems obvious to me that Nate is feeling a lot of pressure to "fit in" when he's on the court, instead of being the offensive spark plug who comes in and tries to score in a hurry. In both cases, Doc has refused to step in and take sides in this team's internal struggle.
Mike