At one point in tournament ball, it was considered a bad thing to be a team hopper. Guess some people got over that quickly. I have had the same 6 girls for 5 seasons, 2 girls for 3 seasons, and 1 girl is a floater. We play A ball and gold and beat the nationally known orgs more than we lose to them...... Sure you will get some turn around at the bottom but no more than a girl or two occasionally. If you are losing that many kids yearly, maybe you should start looking forward instead of focusing on one season or screening your players and parents better. Maybe you guys are doing something wrong, maybe not but I know I certainly am not. Several of the teams around here do it the same way we do and their turnover is minimal as well.
So reading this, you are turning over about 2-3 players per season which matches up with what I wrote. No idea what age group you are in, but the older it gets, the more reasons players leave teams as the 'why' they are playing changes rapidly so even if you do everything right, you still lose some girls.
According to FLOSoftball my DD's team beat two top 20 teams and lost to another by 1 in the last two weeks (not that means anything really but it is something). So I guess we are doing OK.