@Raspberry Plum Yeah, like Karkadan said, the world is stuck in a time loop that it can't escape from and there is an extremely limited path for the world to move forward once again. Earth has become somewhat of a "dumping ground" for karma and causality due to not having a demon king and therefore being the source of summoning heroes to other worlds. Although those other worlds were saved, Earth has progressively absorbed that karma and causality leading to the inevitable time loop it's now stuck in. Now, to break that cycle, Earth requires a demon king and in order to get one, they need to be absolutely pumped full of karma which is created by mass death and suffering.