which was not a good year for USC football was 75,000 per home game. The reason there are empty seats is because the stadium holds 93,000. It is the largest stadium in the Pac 12.
LA has not been an NFL town for a long time (that is until the Rams returned) but 75,000 per home game is not bad considering how much competition there is including rival UCLA which averages 66,000 per game.
And by the way USC has, for decades, owned the LA market in college football. They have, in almost every year outdrawn UCLA. There is a very rabid and dedicated following. USC is not lacking in booster donations. This despite the fact that the campus is situated right smack dab in the middle of South Central L.A. It is this little enclave carved out of a war zone.
The CB perception that USC is weak is just plain inaccurate. The problem is that most other schools in the Pac 12 do not have the same amount of support that USC has.