You seem really worked up by this to the point you’re strawmanning me.

It’s culturally part of it, idk what tell you it’s just fact. Not authored by the same person, not having the same impact probably (although sometimes works by other authors outstrip the original), probably drivel, but valid all the same.

Any other approach leads to weird inconsistencies. Like who owns a character in a group effort? generally in our legal systems a company. That company can persist beyond the involvement of all the actual authors. It makes no sense to then later exclude work they do in their own time using the same characters or settings, or ones ‘legally distinct’ but obviously the same.

Even weirder when it’s one author who loses copyright but then writes ‘invalid’ fan work.

Nobody creates original works, all stories are based on other stories. Sure there are degrees of similarity but drawing lines is a messy thing that even in actual law (which is not trying to be logically coherent) it takes teams to arbitrate and only draws conclusions in self-reference.