There are two:
1. The u of u fanbase is comprised of primarily blue-collar demographic. There is nothing wrong with this and it’s a noble segment of our society. This is evidenced in the Utah advertising schemes: tattoo removal businesses, bail bonds man, dui attorneys, etc. because if this, success of the u of u athletic program is an escape. Now that the u is in the gutter, that escape is gone, thus the extreme reactions from their core fanbase segment.
2. Much of the u of u fanbase hates byu because if it’s affiliation with the LDS church. Their hatred for byu is really hatred for the LDS faith. This is manifest in the mocking of LDS sacrament, baptisms, etc. also their raucous tailgating and west concourse ceremonies are more evidence of their visceral hatred for LDS standards.