The final fifty years before the disaster were like the hour before dawn, the rise of darkness and the destruction of all things. To a mortal, fifty years was half of their lives, but to cultivators, it would only be the blink of an eye.
The powerful warriors of the previous epochs did not want the fifty years to only last for the blink of an eye. They wanted to let all the madness that had accumulated in their hearts burst forth and release all of their desires to their hearts' content until they welcomed the disaster with the world. Then, they would live wilfully for another hundred years in the new world that they believed would appear after the disaster.
Only after that would they fall asleep and wait for the disaster that would arrive countless of years later in the new epoch so that they could wake up again.