After the first half of the season, expectations understandably rose. BYU was not able to meet those high expectations the second half of the year. People would likely be a lot less disappointed if BYU started the year 4-2 and then finished 6-0. It is human nature to let up when you drink your own cool-aid.
Not sure if that is what happened but the team we saw the last 6 games definitely does not look CFP worthy, or even top 25 worthy. All of their top wins occurred in the first 6 games (Baylor, KSU and SMU).
Very good season, but short of a special one.