As Vivian said, it was difficult to reason with people who saw their faith as everything.
Gotarug was likely the oldest and most traditional man in that society of remnants. He had a rich and unique experience as well as ancient knowledge but he also used to attribute phenomena that he could not explain to the goddess. He told Hao Ren about the ancient history recorded in the manuscripts, but Hao Ren would have to deduce the truth of it.
According to Gotarug, the end date of the Sun Dynasty was in line with the time when a significant event happened in the Plane of Dreams. So after the fall of the goddess, the planet and space around it were thrown out of the Plane of Dreams, getting stuck in the Wall of Reality as a result.
The closure of the heavens was an emergency measure taken by the First Born in response to the natural disaster caused by the disappearance of the sun.
