It would be interesting to know how many people get those $80 season tickets that are in the upper bowl. USF always tries to advertise the fact that their season tickets start at such a low price. It looks like their strategy is more about getting people to come to the game regardless of where they sit. If they close the upper bowl, this could hurt their marketing strategy with the cheap tickets.
I'm not saying that the market strategy is working because I have no clue and I'm in no position to say, but I could see this as being a reason why they would not want to close the upper bowl.