Hey Fish, I full on believe that your team held out those starters you mentioned (WR's and LB), as well as did not use/target their TE's against AZ with the sole intention of not giving Utah usable film or well a true game plan to go off of when watching that game. It may or may not be true but that is my opinion, which I do not watch or pay attention to your team so I did not know that until I turned to check the score and see how Samson Nacua was doing (he's way too likeable to still not cheer for) only to find out he and those other starters were not playing.
You can also disagree with me about this next part BUT as far as reasoning; there really was no reason to treat the AZ game as anything but a warm up game for your team. There is no downside if they lost (would be different if they thought they had a realistic chance of going undefeated) as it does not change their season outcome or bowl game and if they did lose it gets the team fired up and potentially gives Utah a false sense of security. To me Utah is your team's biggest game of the season (especially due to the current 9 game streak) and planned accordingly to try and give themselves as much an advantage (perceived or otherwise) in anyway, no matter how minuscule, as possible as they could.