I don't think it is about earning minutes, I think CBS just felt better with guys like Turner and Sullinger than Mickey and Rozier. Nothing more than that. You play the guys you have more confidence in and that you think will get the job done. Period.
And here is the thing, this is much more about roster construction which is Ainge, then coaching which is CBS. You can't just keep adding mid-1st round picks or later and expect them to play. It just isn't logical.