I'd like to help the dev team but i lack time and i have a slightly different vision compared to the authors. Less minimalistic, more fully-featured. Not a game engine, just more complete interfaces. I think that's what is stopping most people using it for other than little games and experiments. I'm using SFML to make a big sound creation software and it works, but some limitations are painful, like the Text class, far from any modern standards. Or if I want to set a View position relative to its top left corner, heh i need to use setCenter and recalculate (it feels strange and uncomfortable for anything more advanced than centering a camera to the player). Some of SFML initial spirit "code it yourself if you need advanced features" just can't work in real world. A bigger community would probably bring more contributors too...
Don't worry i may look negative but i think SFML is still a nice piece of work. It's just hard to get people working and involved on it because time isn't infinite, and too much good ideas are stopped because of this minimalistic spirit.