Same reason that Facebook wanted to buy Instagram for billions....it's a community.
I'm sure any new owner of GAF would walk in (hell, they may even keep EviLore as the guy in charge) and proclaim that absolutely nothing will change.
Of course things inevitably would, but I'm sure that GAF makes money from ad revenue as-is, it's continually growing so it has good investment potential (a clearly demonstrated $5 million -> $10 million increase in valuation from interested parties shows this), and it has quite the reputation.
Its unique attributes (strict moderation, exclusive-club-esque limited approval of new members, a lot of game developers / people in games media who contribute to the site, etc.) really add to its allure.