I think this happens because the publisher owns the content and owes royalties to authors under certain conditions (which may or may not be met in this situation). The reason I think this is I had a PhD buddy who published a book (nonfiction history) and we all got a hardy chuckle at the part of the contract that said the publisher got the theme park rights. But what if there were other provisions in the contract that would allow for this situation without compensating the authors? Anywho, this is a good reminder to read the fine print on anything you sign.