Keywords don't work for self-published books(and they never have). No idea what to tell you there.
Also, selling a lot of books at one place and not many at another doesn't really mean much, either. I know it's a bit strange, but different markets for different storefronts and all of that.
I sell more of some stories on Amazon.com than I do on B&N, then I sell a different set of stories on Amazon.co.uk more often, too. iTunes is kind of all over the place for me, I sell next to nothing on Kobo because it's stupid over there, and Smashwords/ARe change it up every now and again.
It's just how it works, I guess. In terms of keywords for B&N, there's really nothing you can do, though. Just hope and pray for luck, I guess.
During the Pubit! Administration, I found that keywords would work at some times and not at others. It was almost as if they had a switch they could pull, that would turn them on and off but of course it's to their advantage that they work.
I'll also add that since the switchover from Pubit to Nook Press, many of my titles have gone further down on B&N search pages. This may change and fluctuate with time.
I jumped the gun after getting too frustrated. I still have my book on B & N with hopes that it will do well. I received an email from Nookpress stating that they are working on this issue and I trust that they are. I hope they get it resolved! I have sold over 20 books here which is 20 that I may not have sold otherwise so I'll stop complaining and just hope for the best! :-)
I wouldn't worry about the keywords too much. There's other ways people can find your book, too, not just by the title. I couldn't tell you EXACTLY what these are, because I have no idea how B&N's search engine works, but it's not solely based on title or anything like that.
I still manage to sell quite a lot here despite keywords never having worked. Amazon's pulled ahead in recent months, but before that I actually used to generally sell more on B&N than over there, and numbers here seem to be more consistent and longer lasting than Amazon(which I honestly prefer a lot more. Amazon sales are like a flash in the pan sometimes, while B&N is a slow simmer to a boil).
Anyways, yeah, there's no reason for you(or anyone) to pull their books from B&N really. Even if they never sell a single copy, what are you losing by keeping them up here? It's not like it costs you anything, so you might as well, you know?