People's failure to learn is a built-in, inevitable direct consequence of human mortality and a relatively short lifespan. People live just long enough to be allowed meaningful discovery and gathering of experience that they then attempt to pass on before they die - but the next generation brings a fresh set of eyes and the "passing on" bit happens selectively and critically.
Often this is a very good thing, or else the immortal Ur-humans would have concluded long ago that the Earth is flat and the Sun is orbiting around it and that would be that, case closed. This way at least human knowledge gets a chance to progress every time the "old guard" finally kicks the bucket - and no sooner, as often observed with scientific dogma that stubbornly persists for a generation.
On the other hand, it is also often a very bad thing, as people who feel no need to actually fact-check things arbitrarily decide that inconvenient stuff they didn't personally see never happened, whether it's the moon landings or the Holocaust. And every time they think "surely WWII camps for Japanese couldn't have been that bad..." they get one step closer to willingly doing it all again...