The God Burial Valley was turned into a plain field after the restoration of God World. Later on, Mo Wuji executed his Great Art of Destruction and destroyed this place once more.
No one else would be able to find the entrance to the God Burial Valley here. In other words, even if someone did find the entrance, he wouldn't have any means of entering the God Burial Valley.
However, Mo Wuji knew that he might have destroyed the entrance but he certainly didn't destroy the God Burial Valley itself.
At that point in time, his Great Art of Destruction was barely formed. Even now, after stepping into the Quasi-Sage Stage, Mo Wuji was aware of how hard it would be to destroy the God Burial Valley with his sacred art. Moreover, there was still a Resting Land of Gods within the God Burial Valley.
