Evidently you haven't read the hundreds of posts outlining the benefits of being Independent for BYU.
1. Money - BYU brings in much more TV money as an Independent than as a G5 team.
2. Schedule - BYU can put together a much better schedule now.
3. Costs - Other than re-joining the watered down MWC, costs to run BYU's other teams would greatly increase for no benefit.
4. TV exposure - BYU would lose TV exposure guaranteed.
5. P5 conference - IF circumstances ever allowed for BYU to join a P5 conference, those would greatly diminish by being in a conference.
6. Playoff access would not be even remotely guaranteed anyway.
It would be easier to ensure the 'G5 guaranteed spot' was simply the highest ranked non-P5 conference spot.