I have heard it time and time again -- "coaches jobs are on the line so they play the best players so they can win."
However, at the HS level that is just not always true. First, the coach's day job is usually a teacher. The stipend they get for coaching is generally too small to be life altering if they are "fired" from coaching. Second, the "talent" is seen thru their eyes. They may value seniority, friendships, etc.
So the situation in the OP may make zero sense. It wouldn't be the first time.
It is widely known that this HC will not put in extra time if he is not compensated for it, he has told the players that. That is why he will not participate in the summer or fall program.
And you can't have it both ways. You can't preach that you are trying to have a winning season and then be loyal to SR's just because they are SR's when they are clearly not the best player for the position, and in this case not even the second best.