I actually read an article somewhere that said that apocalyptic end-of-the-worlders are fairly immune to being convinced the end isn’t coming soon. When the chosen date comes and goes and nothing happens, they don’t go “Oh, I was wrong” and go back to their lives. They typically simply become convinced that their interpretation was incorrect, and pick a new date.
Most of these people have made drastic changes to their lives, and they also have picked a new social circle (the other believers). These are powerful psychological incentives to remain on board with the program, as I recall how the article explained it.