It’s fueled by many things:
Rivalry
Spite
Bitterness
Jealousy
Politics
Religion
Interactions
And much, much more. But make no mistake, there is no level of failure or dysfunction that would satisfy the hatred here. They would literally dance on our graves.
And you know what? An awful lot of Utah fans feel the exact same way about BYU (not any conference though). It is what it is.