Why? The Chargers aren't that good and the Cards record is a mirage. Not to mention that the Cards fans in general aren't a big traveling fan base.
This was to be expected. Their first home game of the season was blacked out. They are going to be a team which relies on opposing fans buying the rest of the tickets. I believe they play the Pats this season. That should be sold out. As a matter of fact, I stumbled onto Stubhub for that particular game and noticed the same seats where I am sitting in for this game are double the price.
SD fans are almost as fickle as AZ fans. It hinges on the play of the team and the poor conditions of Qualcomm stadium. The Charger FO is dying to get a brand new stadium. Allegedly, they threatened the city that they would consider moving to the new stadium in L.A. if their needs are not met.