Didn't mean to imply one person funds the whole thing out of their pocket, but it's likely that the chairman, Paul Sagan, is both giving a ton and recruiting a lot of other wealthy people. Maybe a quarter or less of revenue comes from donations <$10K. That's not uncommon, but I don't think it's how most non-profits are funded. Either way, my point is that they could not sustain themselves as a for-profit business by just selling ads or subscriptions. And they are very much dependent on staying in the good graces of a small handful of people.