I started looking at just a small specialty site and inviting friends. An open site would be buried by applications and uploads.

The book keeping, to pay people is insane. EU has some specific requirements, the IRS withholding if someone is out of the US, reporting, It would need to be a corporation or at the least a LLC. This isn't "Field of Dreams" if you build it, they will come. Marketing expenses to let buyers know the site exists.

Salary, operations, IT, reviewers, servers or a hefty paid host. Of course there could be self review and if someone spams the site, they could be asked to leave. Legal, and there would need to be an accountant. Who handles customer and artist inquiries?

Who's going to pay to build the site and have the software created?

And finally the nature of Microstock, most people have all the same files on all their sites, so we'd end up with another "me too" site with the same files and people, competing against Shutterstock and Adobe. Why would a buyer come to a site that's smaller, has less to offer and pretty much the same images?

Sure I'd join and be happy with a co op, shared work and income. A better percentage would be nice. You build it and you'll have about 10,000 people who want to join.
 

That's my basic view of why there's not an artist run site. Not impossible or a bad idea, just expensive and complicated.

Next week someone can ask why there's not a artists union to represent us and demand better pay? 

A new site comes along about every month. Most are just fishing and never go live or do more than come here and ask "what would you want". We see promises, big commissions, and most of them never sell anything for anyone. The question would be, if someone started a co op, what would make buyers come? How would people find it. Could a co op actually make enough to pay the members something, at the end of the year? That's right, you aren't going to get paid monthly...