A few reasons KS may want to stay at BYU over jobs like UW.
1) Be the guy who brought a resurgence to a program he helped build while he was a player.
2) Reap the benefits of helping make BYU a P5 program, not just in reputation, but in reality.
3) NIL freedom. Between Utah's lack of regulation on such things and BYU being a private school, he realizes he can parlay this into a major recruiting advantage (at least in the near future).
4) Lack of pressure from heavy hitter Alumni. I know BYU has some strong and wealthy mega-donors to keep happy, but it's not like he has to keep as many prima donna mega-whales or famous alumni happy as he would at places like USC/UW.
5) Less concern for political meddling in football. We've all seen over the last year what differing political priorities can result in from state to state and conference to conference. Again, being in Utah and at a private school, he's in about the most protected environment possible right now.