economics. BYU would lose millions in the move, not counting the loss from donations dropping off a cliff and they would be sitting on season ticket prices that don't justify the means. They only make $5M/year....IMHO they could lose $10M in a hurry and then be a world of hurt.
On the flip side I know there are people saying there are huge donations if they go P5, but people won't give the big bucks on a dream or a whisper. Holmoe is in a very difficult position