It is a varied combination of factors, from my experience. There is a direct correlation to academic work and playing time; when playing time is reduced and work load increases there is a tendency to leave a team. Also studying abroad coupled with an internship, which occurs during junior year, is factor.
There are a lot of programs, particularly new D1 programs, that are recruiting a lot of girls. That makes for a lot of players on the sidelines.
Another factor is just growing up. Sorry parents but be aware--social activities, romance, freedom--whatever you want to call it, is going to be a factor.
