Never forget that Literature is the child of Theatre, not the other way round. Elaborate, sophisticated theatre was being performed thousands of years before the invention of the printing press.
In certain cases the words were interesting enough for the scribes to copy them down. But the remainder, so very much, was lost and forgotten. It may have been wonderful theatre for reasons other than the words. We are left with a distorted picture of what theatre has been.
"The palest ink lasts longer than the strongest memory."
- Old Chinese proverb.
"Language was invented by illiterates. Probably mimes."
- Carlo Mazzone-Clementi