Unlike your OP, I completely agree with the statement the offense needs to improve.
But looking at BYU's last 3 drives where the offense sputtered? (I will do the last 4 drives for kicks, but I know you said 3)
#4 - BYU goes 54 yards in 10 plays and kicks a FG. (The offense did fine, but a TD is better)
#3 - BYU goes 75 yards in 6 plays, gets a Touchdown (the offense did GREAT)
#2 - BYU has 1 play, Run for 10 yards and fumble lost. (Offense didn't sputter, Ropati just dropped the ball after 10 yd run)
#1 - 2 minutes and a large lead, BYU goes 3&out for 2 yards (Offense played overly conservative during garbage time. . . I guess the offense "sputtered here").
Maybe we just have different definitions of sputtering. . . But outside of Ropati's fumble, I think the offense did fine.