Let's just say that you are right about "playing time" being everything, what about 40 plus player high school and 60 plus player college rosters? Players can improve and experience the sport and the team by training and practicing and challenging starters. There are only so many starting positions and so many lines and so many minutes in games. What may make sense, is for coaches to schedule other tournaments, games and scrimmages for the players the consistently get less minutes and give them the opportunity to compete in games.
