The Ghost Domain and the Ghost Path are not the same place.
According to Dan Qiusheng's description, there originally was no such thing as the Ghost Domain between Heaven and Earth; it was the Ghost King who had personally torn apart an entire Ghost Path, creating a domain that could accommodate demons and ghosts without being taken away by the Underworld. Subsequently, Ghost King Jiang Li established the Ghost Market and Ghost Town within the Ghost Domain, the former for demons and ghosts to trade, and the latter to house certain ghosts favored by the Ghost King.
Thus, before the Ghost King's reign, the entire Ghost Realm was merely a Ghost Path leading to the Underworld, intended for humans to be reincarnated. There were no Ghost Markets or Ghost Towns, let alone a place for the ghostly and fierce ghosts to stay.