It would seem your numbers are confirming the analysis I put together for a blog earlier. It would seem that minnows are either choosing not to participate or abandoning their accounts at a rate that is faster than new users are added (churn). I pulled a post together exploring that and offering two solutions https://steemit.com/steemit/@lpfaust/an-open-letter-to-the-steemit-powers-that-be

I see posts coming from the developers about new features, but I don't see any move towards addressing this very serious problem. I am concerned for the future.