We record everything, we store everything. We have videos of everything.
Cleopatra, Julius Caesar and many others became legend through the retelling and deformation of their stories.
Will Barack Obama, Albert Enstein and others become legend 5 centuries from now?
Will there be a funding myth of the Gods giving the internet atop of a mountain to the prophet Berners Lee?
Would Cleopatra be a legend nowadays if we could browse her teenage posts and selfie shots on facebook?
I think myths exist to fill the gaps in our knowledge, in this case our knowledge of what actually happened to Charlemagne and Arthur. If we had detailed and completely trustworthy accounts of what those people did on a daily basis back then, with photos and videos to prove it there would be no myth, I postulate.