Kids don't pan out all the time. Football is a violent, dangerous sport, and there are a lot of kids who play it for the fame and chicks.
When you get to college and start really getting hit, your motivation may decrease. A lot.
And injuries happen.
And Stanford's defense is not great right now. Not at all. And at Utah, they are graduating their two starting safeties.
He could go into either school and push for a starting job right off the bat and get playing time immediately.
The cream rises to the top. And in today's football, go to the school you think you'll succeed at, and if you don't, you can always transfer back to BYU. It sucks, but it is what it is.