Because of how they did in conference play. The team that wins a division is the one with the least losses in conference:
Bama lost 1 conference game at the current moment.
Miss st lost 2 conference games. One of those was Bama, so if the 2 end up with the same record, Alabama has the tiebreaker.
Ole Miss lost 3 conference games. No matter what happened today, they had already lost more conference games than the 1st and 2nd team in the division; once Arkansas beat them, they couldn't catch back up.
Auburn also lost 3 conference games
LSU lost 4 of them
And so on.