Remember the movie Independence Day when all those folks were buggin' out to the desert with their RVs? Perhaps that is what they're concerned about...a bunch of non locals wandering into town to scoop up supplies and groceries. Maybe it's already happening.
I think it's all about keeping the few grocery stores there stocked for their own residents...so they're sending Rangers out to cruise the backcountry? What if you're just passing thru and want to hit the store in Monticello to get some grub?...they gonna give you the evil eye?
Has to be about keeping people away, otherwise it makes no sense. Mormons are hardcore, man.