The reason for that is the strong speculation about the approaching Doomsday. Though scientists and many rational sources strongly believe that it is not going to happen, many are of the feeling that something significant or furious may happen that day just like a prelude to what is about to come.
Few others are stating that whether the Doomsday will happen on 21/12/12 or not, the way humans have been indulging in atrocities and extreme measures on this earth, the day is not far when nature or a divine entity called God will strike with fury and wipe out many. Let us see how much the prayers will help.