There are sites that do this. For example, Tsu did this as a social network. Digitalpoint was a forum that used to do stuff like this with ad revenue sharing, a

There are sites that do this. For example, Tsu did this as a social network. Digitalpoint was a forum that used to do stuff like this with ad revenue sharing, and other forums installed the add on for it too. The problem is twofold: 1. If you're massively successful, then revenue sharing creates huge incentives for spam. Hence you often get people posting links to their content all over the place (especially on rival sites), at which point your brand gets seen as sleazy and your domain often added to a lot of blocklists. You also get a lot of low quality users signing up to post junk in the hope x amount of people click their ads or affiliate links. Digitalpoint got flooded with one liners and gibberish from people in poorer countries and ended up losing most of its more respected users in the process. 2. Revenue sharing often breaks down to a very, very limited amount of money for anyone using the site. Social networks and forums are not the best for ad clickthrough rates or affiliate links, This varies based on how exactly the users are paid (per discussion, per post, per video/image, etc), but it generally isn't enough for anyone to live on unless either got really low expenses or the site itself is ridiculously massive. That's why new sites don't do it.