Planes are probably filling up. 50000 convention attendees over those few days, and I bet the Nightclub and Bar show have a lot of people from the SF area. Fly WN. They can get you there for $77 still, although over $100 out of OAK.
Of course, you could make sure your search parameters on the AS site are correct, and you'll find $56+ on the 26th. The most expensive "cheapest" OW outbound is $116.