You talk about E=mc^2 like it was some kind of Mayan idol waiting for Indian Jones to uncover. In a way I guess that's true. But Einstein wasn't the one who placed it there, so if the knowledge is forgotten then that just means someone else will eventually get the thrill of discovery.
It’s less that it gets forgotten and more that it’s not really useful to the vast majority of people. Most people who “know” E=mc² have zero use for it.
But something like geometry has practical applications that continue even if people don’t know it by that name (most builders know the 3-4-5 triangle right angle trick, for example).
