The gods withdrew from the world due to the deaths of too many gods at the end of the plane of time left all of them weak. The gods would need time to recover at the cost of their much of planes. (Some ceased to exist such as the Plane of Sky, while others were just shards of their former existence) The gods also needed to stop the organized mortal incursions into their planes. To do this, the gods chose npcs to be their avatars and then retreated to their planes removing their direct influence on Norrath after setting in motion several events.