As Phoenix Suns fans, we have witnessed first hand for an extended period of time that young NBA players have a learning curve when they first enter the league. It takes a while for the vast majority to become quality NBA players, if they do.
Although it might sound obvious, the same is true for NBA coaches. It is their first time being in charge of a coaching staff, running a training camp, and creating game-plans and plays for a game. Just like anything else in life all these new responsibilities will take time and repetition to improve.