In Belgarath the Sorcerer Aldur and Belar, after the Breaking, raised the escarpment up to protect their people... though considering how far the escarpment is from Korim, which it is implied they were near with all the people that is fairly absurd. Why they didn't occupy it afterward is a little more reasonable. Most of the population was killed and they went home with their Gods, who were there in the flesh, to set up new realms. Initially those eastern areas would have been flooded and racked by Tsunami, and they're a long way off through mountains, plus it is implied the people didn't like to be too far away from their Gods. And the Arends and Tolnedrans were boxed in by the Alorns - who had plenty of room - and the Nyissans, who are slothful drug addicts. Tolnedra isn't interested in any colonization just trade, and the Arends spend all their time killing each other.

That's all nonsense, of course but it by Fantasy standard sit's passable. In reality long before the Angaraks could have migrated that area would have been totally settled, even if a single hundred-person group settled there, since even the most slow growth civ sitting on empty fertile land is going to double in size at least once a century and they had like 20 of them... 100x 2^20 = 100 million.

That's hardly a screw up limited to Eddings though, there's all sorts of sci-fi where a place controls 'a thousand worlds' and has a fleet of like a hundred ships, in spite of the implication that it means not even 1 in million people serve in their navy and they should be sporting like hundreds of ships a world minimum. Our 'stellar empires' stretching over 'thousands of light years' like that would mean hundreds or maybe thousands of stars rather than tens of millions. So it's not something Eddings had a monopoly on.