I really don't have much idea what was the reason ancient civilizations were wiped out, or Khaneri'ah was destroyed. But one thing is sure you don't put someone under a curse for eternal pain. Residents of Khaneri'ah, like Hilichurls, don't have any memories or signs of intelligence left and have become mindless monsters. From the story, we got to know about the wrongdoings of Gods against the common people of Khaneri'ah and how they have to live a life full of pain, and even in their last moments, they cannot attain peace.