is because BYU is unwilling to open up the coffers enough to hire a coach with head coaching experience, which means whoever the replacement is will have to go through a similar learning curve as Sitake did.
The other factor is BYU does appear to be improving, a solid assistant coaching staff is in place, and Sitake's recruits are becoming upperclassmen just barely this season.
Sitake doesn't deserve an extension, but it might be a good move. 2019 will obviously tell us a lot about Sitake, so the wait and see approach is probably better.