Dean doesn't like the mountains.
He gets that they're supposed to be beautiful, impressive, majestic, something. That people walk up them to have spiritual awakenings and come back down feeling enlightened, or inspired, or purified. Dean doesn't know if that's actually true, but if it is, it's about time some hunters went up all those mountains to see what sort of nasties are hiding up there to brainwash people into spiritual awakenings. A spiritual awakening never did anyone any good. His own pretty much sucked.
( Also, mountains are high up. )