I'm not sure what you're asking, because the badge requirements are displayed right on the page that you linked. They are:
Participated in the definition, commitment, and beta phases of a successful site. This badge can be awarded multiple times.
Did you not see the description, or did you not understand some part of it? Please add a comment or edit your question if I haven't answered your question.
I'm not an admin, so any definition I put forth would be pure speculation. However, I can explain the reason that nobody has a Founder badge yet. Only one site has made it out of the beta phase so far. Based on some of the discussion at its per-site meta, I don't think the team considers it "a successful site" just yet. It's kind of hard to participate in all the phases of a successful site if there are no successful sites, eh?