And, one thing we have been told is that maybe AO wants the wall, to punish mortals who don't worship the gods. But, there is a small problem with that. AO changed the universe to make mortal worship neccessary to the Gods existence as a punishment to the Gods.
So, we have AO making it so that if the Gods ignore their worshippers, they are punished by a loss of power. But, if the worshipers don't worship... they are destroyed for all time by the Wall... on AO's decree? Thereby circumventing the requirement that the Gods actually need to pay attention to their followers, because all the Gods need to do know is say that if you don't worship them you are destroyed utterly, and then they can go back to ignoring them.