It is normal/common for voters or the AP poll to weight recent results more heavily. Teams that are "hot" are going to be ranked higher than teams that are "cold" even if the cold teams did some good things early on. I don't think SMC finishing higher than BYU in the AP poll is odd considering all the factors.

SMC was a hot team that had just beat Gonzaga to win the WCC in their prior game.

BYU simply was not playing their best by the end of the year.