Clark had previously worked at Jacksonville State and didn't want to leave Alabama because he wanted to keep his state pension, I believe.
The # of UAB fans really doesn't enter that much into the calculus here, I think. Just about anybody who pulls for a MAC, Sun Belt or CUSA school has another primary rooting interest, and that's totally okay. The question is whether the administration will release the funds needed for facility improvements, a competitive coaching staff, and recruiting. They did not do that before (the board wouldn't let UAB hire Jimbo Fisher, fix the practice field turf, etc etc), and if they don't, UAB will never win more than 4 games a year and the program will scuttle.
If they actually pay just market rate in CUSA, there is no structural reason why UAB can't be an upper-level football program in that conference.
Wonder when they're actually going to play in CUSA again though. No way in hell they have an FBS roster ready for 2016....