I have been to every A-Day game since 2009 I think. I had absolutely no interest in football before 2007, but decided to watch some games that season and got hooked, so I am a newer tide fan, else I would have gone to a lot more of them. I also try to attend at least one game per year, so I can't say that I am complacent. I would go to them all if I could.
As for others (non-students), you have to keep in mind that there are a lot of factors that go into whether or not they attend a scrimmage game or other games, such as:
1) Not everyone has a job that they get weekends off of.
2) Not everyone has enough financial stability to afford the gas or flight that a trip to T-Town would cost.
3) Some people may have other obligations that they must attend to than a football game (weird I know, but it happens).
As for the students not filling up their sections during the games, I am with others that say the upper deck should be converted to Tide Pride seats. Unless the students are anti-social or really like space, they are going to try and get into the lower bowl to be in the student atmosphere. It wouldn't surprise me at all if some students decide to leave if they find out they are going to have to sit up top. It could also be that a lot of students have other obligations as well such as tests to study for. It's easy to forget that they are in college for something other than filling up the student section at BDS, but it's true. Frat boys also tend to leave early, so that they can go party. Perhaps they should be forced to sit up top if the seats are going to only be for students.