NFL Sunday Ticket is marketed as an out-of-market sports package, and it's exactly that. The NFL considers Los Angeles to be a secondary market of San Diego, so in the NFL's eyes, Chargers games are in-market games, so Sunday Ticket doesn't apply. Sucks, but them's the breaks.
NBA League Pass is the exact same thing. Hornets games that are broadcast on CST are blacked out on League Pass, but games that aren't broadcast on CST are available (ie, the Hornets and Cavs are playing, but only the Cavs TV network is broadcasting the game, so the blackout is lifted because it's an out-of-market game).