I'm a GT fan by default. My dad went to GT so I grew up going to most home games and a few games in Athens when GT was the visiting team. My dad died a few years ago, but I'm glad I spent a lot of time with him and his former classmates on Saturdays. GT wasn't that good in the 70's and 80's but at least they played real competition most Saturdays.
I went to Georgia Southern (when CPJ was the OC under Erk). If they were a BCS program with more coverage, TV time, and if I lived closer so I could go to games more often I'd follow them instead of GT.
The other factor is that I can't stand UGA, which makes GT the logical choice. I'm a fan of whoever is playing UGA.
In the last two years I've considered making a switch, as GT isn't headed in the right direction to compete on a national level. It's not much fun to spend lots of time and money (and emotional investment) on a program that doesn't match my expectations.