IF that doesn't happen on a regular basis, that QB should be pulled and replaced with someone that can. Pulling a QB after a few non-productive series makes more sense instead after a game especially when you can salvage a win.
But IF Tanner (just for this discussion) can't lead his offense to produce TD's, then you go with another QB that possibly can, else BYU will have another long season and from a PR and money generating income POV, the program will be in another year of hurt.