Because of the confidence that game will either instill or take away.
Beat Georgia, and confidence should be sky high and carry them to a 5-0 or 4-1 record. A good start like that will likely get them to 8 or 9 wins by season's end. If they win 9, I can honestly say Kelly deserves to keep his job.
If they lose to Georgia, I see shit spiraling out of control real fast because at 1-1 their confidence will be shot (ND teams always have fragile psyches) and with the challenging road games that immediately follow, they will probably have another 5-7 season. But then it's bye bye Kelly, which is a long-term positive.
I think they lose to Georgia, by the way, meaning 5-7 or 6-6 is most likely.