For a different angle than what other people are saying, I'd argue that it's just because of the particular way the commodification of the arts works under the current system: companies that did nothing but purchase a commodified license that then allows them to commodify the work themselves shouldn't be making money off that deal, in fact that entire deal should be impossible, but because that is the status quo it means that rightfully that wealth that's being generated belongs to the workers who created the commodity in the first place.

That should not be the status quo, obviously. Under a better system this wouldn't even be a question: movies would not be commodities generating revenue, at least not domestically, and would instead be produced with public funding through any number of possible systems; actors and other workers would be compensated for their labor, and potentially entitled to further rewards depending on the reception the work gets, but in a more even and equitable fashion than the current paradigm of a select few people making fortunes (and still being undercompensated because of how valuable movies are as a commodity) while everyone else involved gets worked to the bone for much, much less; any profits turned through international distribution would then go to further subsidize the arts instead of disappearing into some executive's bank account as profits do now.