There is no loyalty of players to their university and vice versa. Coaches have to win, and players want the highest compensation they can get. It's the new world. I know of some high school sports programs doing the same thing to players who were underclassmen, and come the summer preceding their senior year, the coach brings in an out-of-district transfer to fill his spot.
A new roster every year or two is the current reality of college sports and even some high school teams.