You mentioned that all the value comes from investors. That is not strictly true. The money comes from new currency supply via inflation. So that means everyone in the community pays via a slight decrease in purchasing power.
Also if you visit the 'Promoted' section you'll find people who have paid Steem Dollars to promote their posts (click on their rewards amount to see how much they paid to boost their post):
https://steemit.com/promoted/
That currency is burned and taken out of supply. This advertising feature is the key to the ecosystem and is being grossly neglected by the developers IMO.
Full details at: https://steemit.com/steemit/@steemitblog/introducing-promoted-content
RE: Critical Analysis of Steem and Why I'm Invested