My Dad is an alum (sorry, it's "Former Student" there) as well as a former athlete. He has volunteered a ton of time and money over the years to the school, and he was originally from Iowa. The easiest way to explain it is that Texas A&M has developed a unique culture that, when all of the elements are combined, creates a very strong love of the place. People walk around the campus and say "Howdy" to each other. The bonfire (when they used to have it before the accident) was an amazing event. The Corp is very strong there, which I think lends itself to loyalty. The original 12th Man tradition, Bear Bryant and the Junction Boys, the Fightin' Texas Aggie band (which is awesome, if you haven't seen them), all of these things make for a culture that indoctrinates you.
I remember coming to Tech and wondering why people weren't sticking around for the uga game on Thanksgiving, and wondering why students sat down at games, and wondering why people weren't more enthusiastic about the school and gameday. The experience is just more immersive there.