There are a lot of schools who tend to have a % of their fanbase, often LDS, that loathe BYU.

A lot of people hate Notre Dame, nobody hates Holy Cross.

And it has nothing to do with wins and losses. It also has nothing to do with money (okay very little), but as an analogy, if you're poor you tend to be more inclined to despise the rich. And the rich rarely think anything about the poor, which fuels that animosity.

Say what you will about BYU, but in the LDS community it is the Elite school. That always carries a target for those outside the club - whether they could get in or not.