I’m not getting into how long a copyright should last. I don’t have a meaningful opinion on it.
What it seems people are overlooking (or forgiving?) is that the guy published a book about characters (IP) he doesn’t own. Taking something that doesn’t belong to you is theft.
Whether or not Amazon should option his material is irrelevant if he didn’t get permission to use it in the first place. I mean, fan fiction is one thing. Creative license and educational purposes could be argued. But he published a freaking book!
Do you think Zack Snyder should get to put out a Rebel Moon and call it “Rebel Moon: A Star Wars Story” without getting permission or paying for licensing? Is this the reality this sub believes we live in? If you write a novel and I read it and soon start writing better more successful stories based explicitly on your characters without crediting you or sharing in my profit, how would you feel? Should your work be public domain? Is that what you (collective) feel is best for “the public”?
I don’t really have an opinion on what should happen with the work either. I could see some cases where it would be a major loss for the public to have the work erased. This could be catastrophic for classic literature. For something so new and not having any established cultural significance (as much as you wish it did), I’d go with whatever a judge believes is best under the law. You’re welcome to argue the validity of the law, and I may agree with you, but that’s a different conversation.