The vastness of the World of Spirits and Souls was much larger compared to the previously moribund World of Deadly Souls. After all, many places in the latter had become non-existent whereas the World of Spirits and Souls still had a slight opportunity of surviving and some accumulation of Yin Energy.
Otherwise, the Spirit Lords would not need to resort to such schemes and plots and could have gone ahead following Death's example instead.
The river valleys, mountains and rivers, forests as well as grasslands had everything that was needed readily available. However, none of these were living things, and occasionally some spirits, corpses and skeletons could be found.