The memory thing from the Seventh Calamity was explained by member of Sharlayan's Forum in Endwalker.

The Calamity washed the souls of the people of Eorzea on a large scale with memory-type aether, which basically blotted out the memories of the events following it. But no one, not even Sharlayan scholars, know if it was deliberate or just a side-effect.

Quote Originally Posted by Vyrerus View Post
Spoilers for Boss connection.
[DB](spoilers)[/DB]
[HB] is for hidden text, not [DB].