Well sir, you've peaked my interest and I'd love to hear your thoughts. 🙂
I'm not sure if there is a purposeful undercurrent of non-support for athletics per se (I could be wrong here - I just haven't experienced it myself). Edit - I do accept that the downgrade to I-AA in the early '80's could be defined as purposeful non-support - or a horrible decision at a minimum.
I see UNT's apathy problem simply as not having a multi-generational support vehicle like "big" programs have enjoyed. Think of how some high schools around Texas have huge support for a particular program, even when the program is having 1 or more down years. At my HS, it was marching band that had multi-generational, never-wavering support, and the support came from many, many years of success across generations. Some "big" programs also have that type of support (and subsequent t-shirt fans) where kids are born into a generational support vehicle for a program. UNT just hasn't had sustained, high-profile success across generations to create a large following.
Apathy can be overcome (at least short term) by becoming high-profile ... having consecutive 10-win seasons, having a generational win (see App St. vs Michigan), having a Heisman candidate, or maybe a high-profile coach (see Colorado). I hope UNT hits on one of these eventually and then starts the process of larger-scale generational support.