The original statement was about there being little incentive to create a work you don't "own"

Difficulty in copying is irrelevant to owning it.

Moreover, this does not address music or spoken word. A pre-copyright musician can just listen to a piece and play it in the next town over. A poet or storyteller can just memorize a work and retell it.

>> previous comment said "Copying was prohibitively expensive."

I think this statement does have important truth value in it! Copying books used to be done by hand (someone writing manually). Then printing press came, which lead to problems. And that is when copyright concept and law was created!

PS: IANAL and nor a historian. Just sharing my current understanding.