Copyright (and patents) exist "To promote the Progress of Science and useful Arts, by securing for limited Times to Authors and Inventors the exclusive Right to their respective Writings and Discoveries."
The purpose is to promote the progress of science and useful arts for the public's benefit, the means is a limited time monopoly.
The limited time rights are intended to be the minimum necessary to incentivize people to create for the public's benefit. Originally this was 14yrs, required registration, and could be renewed once.
The intent has been twisted by those with an interest in perpetuating copyright indefinitely (rights holders). Now copyright is 70yrs after the death of the creator or 95yrs after publication for contract work. [0]
Why does someone need to be incentivized to create after they're dead? Why were these extensions retroactive since you can't incentivize someone to create something they've already created?
This has been argued in the US courts, the end result of these extensions was because each one is still for a 'limited time' they're okay - even if they're repeatedly extended at each expiration. This isn't the original intent or spirit of copyright law.
> "Pirating it now deprives the owner of some amount of ability to make money from it in the future."
The rights holders have lobbied to twist the law for their own self-interest and then play victim - I have little sympathy for that.
I think if we had something sane (5yrs, maybe special protections around certain types of adaptations, maybe longer time frame to reward authors specifically up to some dollar amount if adapted for-profit, restrictions on for-profit distribution by third parties?) the law would be more aligned with its original goals and there would be fewer issues.
Today you can't even declare something 'public domain' if you want to since copyright is reserved by default. The best you can do is license it permissively.
[0]: An aside, at one point it was until the author's death. This gave me an idea for a B-movie where a serial killer goes around taking out pop groups so their music goes into the public domain.