Simple: money. The money earned from football events pay for so much of that institution's budget. Friday Night Lights is a tradition that's not going to change.
There’s some unsubstantiated claim that constantly growing expenditure on sports is requires like a marketing arms race to advertise to potential students, but I haven’t seen much data backing that.
My guessis that, just as with most professional sports clubs, college athletics programs by design are intrinsically huge loss leaders designed to be vehicles by which coaches & administrators extract money from the university.
For the tiny fraction of top teams with massive fan bases, they can get away with this while being profitable. For almost all other programs, they burn through money chasing success and profitability for a while, and after enough consecutive seasons of financial losses, they retreat to fiscal austerity and a decline in the athletics department while some other programs are on an upswing.
People also like running, video games or chess to name a few. Football, even with its popularity, is unique in providing an enrichment pipeline from high school to the pros that a few benifet from quite a bit.
