My son played several seasons already. We always get assigned to different coaches, with different players. We always request our coaches-- but it is hard to be selected by these coaches, unless some of our friends volunteer coaches. I am not sure if you volunteer assistant coaches or team parents would help or not. It certanly hleps more if parents voluenteer more.
Some coaches have volunteered for a long time, it could be a lot of kids want to be in his team. The city has to also balance out teams.
Moreover, each season finishes quickly. There is only so much a coach can teach the whole team. If your son is very interested, get some private lessons, go to camps, seek out clubs, etc.