He was left a full cupboard by Urban for offensive talent. He's struggled to recruit offensive talent ever since, and that's without having the honor code to deal with.
Speaking of the honor code, either Kyle would have left in a fit of rage, or he would have been forced out because of his fit of rage after he'd lost one too many players to an honor code offense. And BYU would have been left starting all over again from scratch.
Kyle has proven himself a very good football coach. He'd have washed out at BYU in 5 years. Just not a good fit. He made a good choice to stay at Utah.