If we are talking early early then it was because art wasn't a form of "art" it was a form of communication.
But a little later down the road, people did not understand the human body and could not paint one perfectly, and also painters loved to show perfection, as in, gold everywhere, or a kind a top a thousand bodies. Something like that. So yeah...
He three most common musical parameters used are the rhythm, the Tempo, and the key signature of the music.
