Originally Posted by
Cleretic
For what it's worth, the actual explanation given for this is that the Ancient ruins on the Source were destroyed over time by the Calamities. All they had to survive on the First was uncountable years of neglect and natural erosion, and even that did a number on Amaurot, although Anamnesis Anyder managed to stay intact.
On the Source? They had to suffer through six different planetwide cataclysms, including a great flood, an unending blizzard, and colossal windstorms. It's not that the Sundering hit the Source any harder; it's that afterwards, the Ascians hit the Source with enough force that they likely wiped the planet clean of any conclusive evidence of their own society. Which is... kinda tragic, actually.