Attendance isn't as big a factor as it once was.
20 years ago it was a lot different. Not every game we played was on television and even if it was the average person had a 20" tv and it was much more fun to be there in person.
Today 60" + HD tv's are common, every game is on TV somewhere, and you can save the $4.00 a gallon fuel, $20 parking, hours of hassle driving and sitting on the road in traffic, beat the weather in your own living room, and do the 50 other things we all do on weekends these days like taking your kids to the soccer game, mow the grass, go to the hardware store get the widget to fix the what's it, and still make it home in time to see the game.
Right now every sport has the same problem. NASCAR at Bristol sold out for how many years until recently?
As it is now the TV revenue shared by the conference teams is keeping the University paid, fat, and happy. Buts in the seats are just a bonus.
40 years ago the University cared more about the local economic impact of the games a whole lot more than they do now for a ton of different reasons chief of which is it used to be controlled by local business people who were the trustees. Not so much now as it was years ago. The majority of the Trustees don't live within 100 miles of Knoxville.
I'm not sure that 100,000 seats today is as practical as it once was.