The DAO is not getting anything from this AFAIK. Somebody correct me if I'm wrong.
It's a zero sum game. If the DAO were to start buying and renting out cards then they would be competing with people who buy cards to rent out. You don't create FOMO for cards by increasing supply. Even if they don't sell the cards, it affects the market. The card rental market is connected to people buying cards for speculation thinking they can rent it out to recoup their "investment".