From having been an assistant coach on a high school team, it is my experience that most teams that mix up their defenses are typically not very proficient at any, that's why they change them up so much.
I know that JC teaches all the man defensive drills (shell, defensive series, etc.) so it's not that he is not trying to teach it.
But frankly, team defense is kind of like o-line play in football. If one guy misses his block then the back gets tackled for a loss and everyone looks bad.
If one guy allows dribble penetration, or doesn't hedge the screen, doesn't block out, etc. then teams are able to run their sets easily and get good shots or get easy put backs. The key to team defense is everybody plays with discipline and trusts the other players to do the same. This team does not trust each other defensively, you can see it in their lack of communication and that kills a team on the defensive end.
On offense, plays break down but guys make individual plays and you can still score the ball, defense is not that way, unless you have a guy like Blake in the paint that makes up for a lot of defensive issues.
It's tough because man is the way to play but at the same time, you are trying to win and zone may be the best defense right now for this team. It's an awful spot to be in for sure.