Thats just part of the game. I know 1st hand that lilltle league and softball work like this: There are always a core of 5-6 players that play every inning. All the rest fend for themselves and try to get in when they can.
I always tell my son that no matter how unfair it seems (and it is), never question the coaches decision. And no matter how tempting it may be, you as a parent should never question the decisions. If it really bothers you that much, maybe a change to another team or league would be in order.
I do appreciate coaches taking time out from their personal life to coach, it is a hard job.
I know its bullshit, but so is life and I tell my son to use it as motivation to better his skills and make people notice.
This winter, he wants to build his skills, get a little bigger, and become the best player he can be.