The answer is very simple, people gave up and left. While I first joined in 2016, I never made my first post until back in January, and after 3 months of being here, its easy to see why people find no value in this platform and simply throw in the towel.
While I really like the concept of Steemit, and the people here are generally very social and friendly, I see very little prospect of earning a living here based on what I've already seen. You can produce high quality content and never earn a dime here, its a gamble if you will, and there are no guarantees of anything.
From the perspective of being a social network, I think Steemit is great, and the blogging features are a huge plus. Even without the prospect of earning it does hold some value for its users, but people shouldn't expect to earn much of anything either.
It seems the only accounts who manage to prevail monetarily are the ones the platform explicitly chooses to upvote, and those who invested their personal money into it. If you had tens of thousands of dollars to invest in Steem Power, I could see one earning a good return on their investment, the rest wont be so lucky.
RE: How Many Total Accounts Are There on Steemit? Active Users?