Let's say the rest of the season goes well, and BYU stands at the end of it 10-0. (Acknowledged, by the way, that this is still statistically less likely than BYU dropping a game somewhere along the line.) BYU stands at #6 in the polls. It has all but clinched a NY6 appearance.
Then the phone rings. Cincinnati, having clinched the AAC championship the week before, is also guaranteed an NY6 game. But they are undefeated and ranked at #5. It is proposed that BYU and Cincinnati line up a game the week of the last power 5 conference championship game. The winner is, for all intents and purposes, guaranteed a spot in the playoff. But if BYU loses, its lone blemish will almost certainly knock it out of NY6 contention.
In short: BYU can accept the NY6 game, or it can roll the dice and play a game that will either get them into the playoffs if they win or knock them out of an NY6 game if they lose.
Which would you do?