Population Migration / Travel
As the land dried further and further many pleaded for the gods to help the extraplanar creatures in preserving it. However, the gods were still weary of anything to do with the outsiders and in the end, people outright rejected them and anger grew to the point where the gods had to either fight or flee.
It did not take long to realize that the outsiders could not contain the spreading of the desert. Despite this, the gods never stepped in nor did they ever interfere. Some believed it to be that they simply no longer had the power to do so, others that they wanted to punish mortals, yet others that they were not willing to help outsiders. Whatever was their true motive people soon grew angry at the inaction and in the end many tried to force the gods to do something. This did not end well after a mortal lover of a god died during a kidnapping in which the perpetrator wanted the gods to take action before the mortal was returned. Sickened with the mortals, the gods decided to leave for other places. Many believe they headed north, but no one ever saw them again for almost 200 years.