With limited population numbers to begin with Hyrule would go into a state of "Amnesia" after any war spare the Koroks or Kakori who would naturally be the Keepers of knowledge not engaging in war and living a somewhat "secret" existence.At least with Breath of the Wild, It's understandable that most of the country's history is lost.
(they become the master swords "caretakers" after all at some point).