Bad managers.
well, it could be. But you have to admite it's harder to promote or be competitive in those leagues. So, you
need to spend more time. And that's (I think) the main problem. Most of the managers don't want to be conected to BB a lot, so they prefernot to continue in the game. At this point, it's BB creators who have to do something if they want this game to increase the number of managers and, thereby, developing a better game.