To continue, most people who believe the world will end believe it because it is part of their religious lore. Many different religions have this belief. Most people who believe this think that the end of the world will be a good thing, because it will mean that the world is saved, and good things will happen to those who believe in the religion.
They look forward to the end of the world, so they are always predicting it will happen. They want it to happen in their lifetimes. I think that these predictions help leaders get their groups more tightly bound together. They must prepare for the end. As such, the prophets gain more power, which is probably something they like. Followers get a strengthened sense of belonging, and being special because they are one of the few anointed.
It’s mainly an organizing technique. You set up an us vs them scenario in order to whip up fervor. It is used in conjunction with brainwashing techniques, such as isolating the group from the rest of society, and constantly drumming the same message into them, and giving them a sense of purpose. It is a central idea around which organizers can bind followers more closely and make them work as hard as they can.
One problem with it is that when the day comes and goes, the leaders look sort of foolish. Some of them try to explain it away, and say the end of the world is still coming soon; they just missed the date. The brainwashed may still stick with them, depending on their other options in life. In any case, it is usually a fringe idea, and I don’t see that changing much.