There appears to be two things which are hitting STEEM at the same time. Based upon the metrics, it would appear that disillusioned minnows are either not participating or are abandoning the site faster than new accounts are generated (churn). I wrote an article about it and two proposed solutions https://steemit.com/steemit/@lpfaust/an-open-letter-to-the-steemit-powers-that-be

The other issue is the drop in the value of STEEM. There was a really solid fundamental analysis by @hisnameisollie which explains why the drop is happening and he termed it the Push Pull effect https://steemit.com/steem-help/@hisnameisolllie/the-push-and-pull-effect-of-steem-power-incentives-why-the-of-steem-held-in-steem-power-will-tend-to-90-overtime

Hope those two article s provide some answers.