Here's another reason: Our kicking game.
You asked to give a reason why UCLA beats BYU. I'm guessing we're talking hypothetically here. So
IF UCLA were to win Saturday, home field and our kicking game are two reasons I'm GUESSING. We could start another thread on one reason BYU beats UCLA this weekend. If that were the case, I would probably give two: Execution and coaching (see UCLA's inexusable losses to Notre Dame and Florida St. last year)