Earlier quoted context omitted.
You could say that if no users would join Diaspora. Yet, more come constantly, so you can't say that it didn't gain traction.
Joining Diaspora doesn't count for much in itself. I just checked and I have nine "real life" friends on Diaspora, but the last time any of them posted there was four months ago. Posting there is basically posting into a black hole. I used to post there and do the "share on Facebook" thing, but that doesn't seem to have worked for a while.
I have barely any contacts there whom I know personally or knew before I joined Diaspora. Still I find Diaspora conversations with many different users engaging and don't see it as a black hole by any means.
You are trying to compare it to Facebook, which is wrong. Massive user base of Facebook makes chances of finding familiar contacts there way higher. You can't expect the same thing in Diaspora which is a very young network. I see Diaspora as a place for conversations and ideas, not as a place to find people whom you already know from before. If you approach it the right way - you get a lot out of it.
Also, you have to master using hashtags if you want to have any meaningful feedback from Diaspora. Using it like Facebook will result exactly in black hole experience you described. So try changing your mindset when using it. Diaspora is not a Facebook clone.