Fan works promote the idea of collective ownership. There are strict social rules on acknowledging the authorship of a work but no love lost when ideas from individual works are lifted and reworked. This is especially clear in the “inspired by” tab on archive of our own, a popular fanfiction site. By ownership I’m thinking in the legal sense, I think social sentiments around owning ideas an profiting off them directly will change with it and hopefully, overtime, copywriter laws will too to be more forgiving surrounding derivative works