The missing link you're looking for is free copying.
Easily copied art that was supported by a capitalist model, where the artist paid for rent, food, etc. by selling the products of his labor?
Correct, that didn't happen.
Easily copied art that was supported by a capitalist model, where the artist paid for rent, food, etc. by selling the products of his labor?
Correct, that didn't happen.
Yet art still happened ... thus art doesn't depend on copyright.