Yin Death Vortex was located in True Morning Dao World, but it was a region completely separated from it. Even when True Morning Dao World's will was at its strongest, it could not interfere too much with Yin Death Vortex.
This could be said to be a world completely different from the world outside. Cultivators could enter this place, but most of them would have their cultivation bases suppressed. There were also other unnamed dangers in it.
But it was not like there were no life forms who tried to get out of Yin Death Vortex either. However, they were rare and few in between over the course of countless years. The level of difficulty could be seen from how hard it had been for Su Ming to get out in the past.