Please note I can only speak to
my own experiences with this
where I live. It may be very different elsewhere.
The whole A Team/B Team concept may be well intentioned, but in reality, I'm not sure it's all it's cracked up to be. Often, at least in the younger age groups, a lot depends more on who you know than what your skills are. As kids get older, the differences between the teams become almost non-exisitent, and here's why.
As kids move through the age groups, they change. Some get better and more passionate about the sport, and others, just the opposite - some spreading themselves very thin with many sports and activities, not making games and practices and such, and others concentrating on just one sport, the latter naturally becoming better. (Attitudes also play an important role in sports and kids attitudes can change at the age group we're talking about, often in a big way.)
Yet once an A or B Team player, always an A or B Team player, and for a variety of reasons. You could very well have a player who, at 10, was a B Team player, but by age 12 or 13, after working very hard at the sport, is now an A Team player but is still on the B Team. And vice versa - an A Team player at 10 but lack of practice and enthusiasm for the sport makes him now a B Level player at 12 or 13 yet still on the A Team.
So why not move? It may not be so much that the player doesn't like a different coach, but that the player is most comfortable with "their" coach and teammates and doesn't care to switch. They have a history together. And the coaches feel the same way, having groomed their players, they're happy to keep them. Even among coaches, it's competitive.
I have also seen coaches become so nutty that nobody wants to play for them anymore, so those coaches wind up with almost all new players
every year so what may, in concept, be an A Team in reality becomes a C team, lol. Cause part of becoming a great team is learning to work together; it takes a long while to jibe as a team. So players and coaches who've been together, say, for years, could very well have better skills than a brand new team, and this may well be the B Team with better ooutlook and coaching.
I agree young players need to learn to play with a variety of coaches and styles if they're going to succeed. However, sometimes if a coach is too far out there, nobody is going to want to play for them and worse, players will lose enthusiasm for the sport. There should be a good balance of fun and discipline, ideally.