I don't know if the content of the game has something to do with the fact that BuzzerBeater "only" lists 50k users, but IMHO the marketing around and in BuzzerBeater doesn't help its growth.
What's the point? The point is that BuzzerBeater "pretend" to be the best basketball management simulation in the world. The main aspect of these kind of games is that managing a team means giving a life to team we manage as players. It means appropriate or create an identity in which we recognize ourselves. It's the base of a management game. And it's one of BBs weak point. They tried to bring some improvements through the supporter package but it seems like the tool has met its limit.
Secondly, community is what brings people on the Internet. Whatsoever on social networks, professional networks, on line games, Internet users surf on the Web to share, learn, exchange with others around a subject they appreciate. For BB, it is about basketball. But once again, IMHO, the community aspect is one of BBs weak point. The forum is atrocious and leads to bad communication between users. Internet users wants everything right away, and doesn't have the patience to wait for informations. Virtual behaviors are completely different from the real life.
And finally, the browsing... For a new user, browsing on BuzzerBeater must be incomprehensible. You got infos on your left via the menu, on your top right through the drop down menu. And even on the score bar. You see infos everywhere, anywhere, and when you are not used to it, you may feel reticent to pursue the journey...