Its an authoritarian cult. I dated a Mormon girl for a while in college so I got a long first hand look. Upstanding people but not living in the real world of 2016....
They will do what Elder Mitt and his associates tell them sadly.
Admittedly there is a bit of an echo-chamber going on in the Salt Lake/Provo area. They really loved Romney (partly from his “rescue” of the Olympics), and wanted him to win. There is that white horse thing, too.
Outside of Salt Lake, and especially outside of Utah (might need to add Idaho and Arizona to that), Mormons are more open minded, and are not as stuck in the echo chamber.
But even with that, I will be shocked if Trump gets less than 50% in Utah.