So, basically, a random site from their index of ~30,000 sites. You can choose similar sites by index. But what are the criterion to have your site listed her

So, basically, a random site from their index of ~30,000 sites. You can choose similar sites by index. But what are the criterion to have your site listed here, or how it will prevent this from just becoming a massive gamified advertising index, or anything more about "why these?" is not obvious to me. Can anyone explain what is special about these sites specifically, or where this project is going?