The problem with end-times predictions is that they're so obviously made-up. The Bible has lots of dates and numbers and symbols, but it doesn't have a consistent or clear guide for defining them. So it's easy to come up with a calculation that conveniently places the end of the world on a date within our lifetimes. No one ever believes that we're just another generation that will come and go without seeing the most momentous event in human history... it has to happen in our day!
I recall hearing or reading the calculation that Harold Camping used to determine that the end would come in 2011. It was so odd and unintuitive that I couldn't believe that he ever thought it was legit. On the one hand, self-delusion can be very powerful. On the other, I can't imagine a person being that deluded for so long. But I think a lot of the people who make these predictions really do think that they're on to some amazing hidden cosmic secret. It sure beats convincing yourself that you're really Napoleon.