You falsely attribute a niche's draw to the fact that it's niche. I find it unlikely that people would base their interest in a game on its popularity, or lack thereof. If the game is fun, people will play it. If it's not, they won't.
Maybe DF being a niche helps in some way. I don't know. But I do know that the UI is, almost objectively, not good. I know it's why I stopped playing. Once you get more than 20 dwarfs or so, managing who does what is ridiculous. (at least without external tools. I think the popularity and almost necessity of some external tools really does show that the UI can be atrocious at some points. (also note this is not a comment on the ASCII nature of the game, that's fine))
While the interface puts many people off once they are there, would the game get quite as much discussion if it was much more like other games rather than being somewhat more unique (for better or worse)?