I was really impressed with BSU's defense, they played OU as well as any team in the Big 12 for most of the game. But it was clear that at the end they were gassed, because they simply didn't have enough depth. They knew they would not stop OU again, so that's why going for the win when they did made the most sense.
Yeah, BSU's offense didn't help the defense out much in the 2nd half. In the 3rd quarter the defense was on the field more than 10 of the 15 minutes, and BSU ran only 12 plays to OU's 24. The 4th quarter would eventually end up more even, but BSU stayed on defense most of the 1st 9 minutes of the 4th. And of course the BSU offense didn't score a point in the 2nd half until the final few seconds.