hates the church generally. So for many, Ute fandom seems to be a convenient way to indirectly express their hatred for the church. You can tell these by the obvious fact that they hate BYU more than they like Utah.
There are some very faithful LDS folks in that fan base too, which is sad because they let so much bigoted stuff go unchecked from their fanbase.
And some Ute fans are just normal sports fans. Nothing applies universally. A lot of anti-Mormons or ex-mos are Utah fans. But a lot of ex-mos are great BYU fans too.
There is just a much higher percentage of bigoted folks at Utah than you’d ordinarily get at a school that is made significantly up of the religion they hate. Some are less bigoted and more just idiots in general. And some of those are vocal enough to make the university famous within the BigXII and their notoriety is expanding.