I remember Nick Saban saying that a team can only get up for so many games a year. I suppose psychologically you can only go out there so many times before your mind and body become battle weary so to speak. This isn't really an exaggeration, it's been said that playing a football game is like a car wreck. How many car wrecks can you go through in a year before it starts to slow you down?
It's easy to forget that these players went through a ton. It was a battered and bruised team, that played the second most difficult schedule in the nation. No other playoff team had that to contend with, even for Ohio State and Oregon, who played in the additional round, they still played a far tougher schedule.
Add to that the fact that Alabama, even if they won had another playoff game on the horizon, something they never had to deal with before (it simply isn't fair they had to play the first, considering how more they had to do to get to that game) and yeah... I can see why they might not have been up to the task mentally and physically. Most of the SEC was worn out by the end of the season, it wasn't just Alabama, they'd beaten themselves up pretty badly. Is that an excuse? I suppose it is, had Alabama overcome that they would have overcome far more than anyone else had to, that much I know.