Real Talk, alot of ya'll niggas gave up way too fucking early. I've already gotten like 5 players interested, am starting a college scene, and have gotten good players around my area to start playing MB more. Go out there and actually do shit already, and stop crying already!
Speaking as one of those new blood players, I can give my two cents on how to get (and
keep) some people interested. A lot of this comes from other message boards thinking about how to attract new players, as well as what I personally think.
More exposure would definitely help. Now, the fact that MB hasn't been released for consoles outside of Japan is not anyone's fault, but it's gonna make it that much harder to get people in the West to even hear of the game. I think there's been more exposure to MB lately thanks due to its presence at Evo, but I think even just having a setup or two for MB at smaller, local tournaments can probably help at least make players aware that the game exists.
If possible, try to get more than one person interested at the same time. I think people enjoy having someone to learn the game with them. Personally, I started learning MBAC this past summer, and I actually got another friend of mine to play at the same; that way, we both had someone on even ground to spar with, instead of always getting our butts kicked by my friend who was teaching us to play. It also helps players not to think that "there's nobody to play this game with."
And I think Rokunaya has the right idea. For people who are in areas where there are a lot of potential players (large universities, cities, or scenes with a lot of other fighting game players), definitely be more active in looking for people and showing them the ropes. And that's probably one other thing, I think that a way to get players to stay is to just help them out. Might sound like common sense, but just playing matches with them and giving advice can help players not get discouraged, especially in a scene where it seems like a lot of players are unreachably high-tier (maybe that's not actually the case, but again, impressions are a HUGE factor in keeping someone's interest).