We just have a naturally distributed fan base. BYU represents the Church (for better or for worse whether people want to admit it or not) so most members that care about sports have a natural desire for them to do well (or at least an interest in them even if they don’t care that much).
It’s similar to how people in a given state have a natural affinity towards a state school. I was enamored with Colorado when I was growing up when they were good. I’ve since become more indifferent for several reasons including an unhealthy obsession with BYU, Colorado sucking, and having lived out of state for years. I do follow them a little more now that I live close again.
Utah does have a small extra natural affinity due to being anti-BYU. But I think state schools generally don’t have a ton of national alumni and don’t normally have out of state fans that care otherwise.
We do travel pretty well but we also usually have quite a few that just go to games when they’re close.