In recent years over 400 players have been transferring each college basketball season. With 347 Division I teams, that's more than 1 player per team per year. If the number of transfer per team were represented graphically, the most likely shape of that graph - like a lot of things in life - would be represented by a bell curve. On one of the extremes would be programs who haven't been affected at all by transfers. On the other end would be programs extremely affected.
Interpreting that data, however, would lead to speculation. It would be easy to say the former teams have stable coaching staffs who are honest and easy to relate to. Meanwhile, it would be just as easy to speculate that the latter teams have serious internal issues.
But without evidence, it's just speculation. It's possible that a team which has lost a ton of players is just an outlier. With 347 teams, it's natural that a few would be outliers. Weird things happen.
With that said, what in the world is going on at the University of San Francisco? Head coach Rex Walters lost six players following the 2011-12 season, and after this season he's lost four more.