I'm sure there is a political component. The Wilson family was really pushing for Zach to start at BYU as a FR, IIRC,
and I'm sure the same was happening with Isaac at Utah. In other words, it's entirely possible he's not as good as the other people in the "QB Room" that are healthy, but they decided they'd better ride him for the future, or lose him if the Wilsons think he is going to be better off playing 3-4 full years or whatever.