The world in which you speak of where art existed outside of notions of intellectual property meant only the wealthy and well-connected could be artists, whereas with copyright a cancer-fighting, aging, midlist author can still demand royalty payments if Disney bought his books and are still selling them for profit (Alan Dean Foster, specifically). Peter S. Beagle (The Last Unicorn author) was put through elder abuse and lived in poverty, and only many years later was he able to regain rights to his work back as well as force recompense for harm committed to him- this wouldn't work if the rights to his work expired while he was being abused.