When someone creates art, copyright says that there is a countable result we can refer to as their "work". Copyright also says that that artist has a monopoly over the distribution and sale of that work. The implication is that the way for an artist to get paid for their labor is for them to leverage the monopoly they have been granted, and negotiate a distribution scheme that involves paying them.

When an artist chooses to work outside the copyright model, that means they must predetermine part of their distribution negotiation. That might be the libertarian option (gratis distribution with no demands), or it might be the copyleft option, where the price is demanded, but also set to 0. The artist may find payment for their labor by other means, but that's challenging to do in an economy where copyright participants dominate.