That’s an oversimplification. All works are derivative to some extent. There’s a huge difference between taking inspiration from something, to taking the characters and setting from something. Particularly if you’re intending to make a profit.
If an author makes something that a large number of people enjoy, why shouldn’t they be able to make money off it for the rest of their life? Why exactly should an individual give up the rights to their creation simply so that someone else can use their characters and their worlds?
To be clear, I’m talking solely on an individual level. I think the system we have where a corporation can own an idea is very broken. I’m also talking about this from a perspective of the world we currently live in. In an ideal world where money wasn’t the endgame for survival, ideas would flow more freely and nobody would need to care. But that’s not the world we live in.