TBF, there are a lot more things we need to learn and memorize today than back then.
I sincerely doubt this. They didn’t have easy ways to take notes, they had to memorize everything. Day-to-day living was more complex then, not less.
That meme of pushing one thing into your head and losing another is not real. The more we exercise our memory, the better it gets.
How many phone numbers do you have memorized?
Never mind the fact that lorekeeper was an actual job back then - so you’d have people who’s entire livelihood/societal role was remembering these stories.