literally 90% of human history has gone unrecorded, and what has been recorded usually gets destroyed, ransacked or deliberately destroyed, Caligula’s pleasure barges, Tower of Babel, Library of Alexander. Humans have tried to keep knowledge retained. and some people take that personally.
remember when ISIS was at its peak they were just destroying artifacts like it was a kid in a candy store. And that’s just been in the 35 years I’ve been alive.
when Rome fell it took another century for civilization to rediscover the technology and applied lessons used then.
and im a dumb idiot, I’m just making a broad skim, if you could ask a historian they’d likely tell you all the things humans have lost, purposefully destroyed or forgotten along the way.