Trom said it. It is all about situations.
If GB was down by 21 they would have needed to go for the TD. Since they were up by 10 there is no need to push it. You saw what Rouse did in a similar situation. TN was at the 11. It was 2nd down. They were trailing and it was late in the 4th Qtr. He ran it back. Better to be up by 10 or 13 than only 3. TN had to go for it and got burnt. GB didn't have to.
Keep in mind if they were out at the 35-50 GB may well have passed the ball. Once you get down inside the 15 it is really hard to pass the ball for more than 5 yards as there just isn't very much room and the defense knows that. It is a lot harder to get 10 yards from the 15 that from the 40.
I do not remember if he was forced out of bounds. If not, the run would have kept the clock running. By the time you get into that point of the game and you have the lead and the ball you want to keep the clock going as much as possible.
One final thing. By running the ball it is now on game film. GB's upcoming opponents have to consider that the run is possible as they prepare for GB. It may not be very probable but they can not say that GB will pass 100% of the time. There was little risk by running and had a lot of benefits.