I don't think that that is necessarily true. Yes, BB is a long-term game which may not attract a lot of people. But I don't believe it's true that there are not at least 50k persons out there, who would enjoy this game if they really got to know it. In my opinion there are two main reasons as to why BB no longer are attracting new users:
1: Layout. The game simply looks old. The website is in desperate need of an overhaul. We need the website to look 'nice' when potential new users visit it for the first time. In addition, it should also be made suitable for phone use.
2. An app! My personal view is that this game's biggest problem is that we don't have an app. We just have to face that people use their smartphones. And yes, you can just play in your phone browser, but the experience is just not good enough. I think an app would recruit tons of new users through exposure on AppStore and Google Play, whilst notification would furthermore help to keep these new users in the game.
Do these things and I'm sure we would finally see the game grow again