8)The coach doesn't know what they are doing. (Parent could help out said coach Im sure)
I think this is one you might have broken into a few different models:
1) The team is not competitive.
2) The coach is better than you, but not better than other coaches
3) The coach is not a good personality fit for your kid.
4) The coach doesn't know what they're doing.
4a) The coach knows what they're doing on a baseball field, but not a softball field. They spend endless practice hours on 400 foot, 3 throw outfield relay/cutoff plays and 6-4-3 double plays, but never bother to go over bunt or slap coverages.
I agree that girls leave every season, and in a healthy team that's getting better, dropping the bottom 2 or 3 on your roster and added 2 or 3 at the top is a pretty normal cycle. Sometimes a kid will improve more quickly than the team she's on, and sometimes the team gets better and a player who was a core team member can't keep up.