Unfortunately, I think it is probably too late in the season to hope for much change.
I do think it was a huge mistake to not try and develop Carter, Ashton and Cooke more in the non-conference games. There were opportunities there where you could have played one of them at a time in with the remaining starters and hopefully developed them a little. If nothing else, at least build their confidence and learn what they need to improve on. I'm not sure what this coaching staff saw in the past stats that made them think these starters could increase their minutes by as much as they are being asked.
The one that surprises me most is Cooke. I can't figure out what is going on there. I wonder sometimes if he is still hurting (like Naz), or does he just not get enough playing time and his confidence is shot, or is his attitude bad because of the lack of playing time. Remember, this is a guy that played 26 minutes per game for a Pac 12 team, and shot about 46 percent from three. Not a huge scorer, but obviously a better player than he has shown here, and he was a freshman then.
You can't have more than one of the 3 in the game at the same time, imho, and it is difficult to see anyone that could spell Monte for a few minutes, but it seems like something should have been tried long before this.
I'm sure the staff has worked at developing them in practice all year that doesn't mean they are ready to play big minutes in a game.