Why does the concept of "public domain" actually matter though? It's clearly a legally frought concept, and nobody actually believes in public domain itself as

Why does the concept of "public domain" actually matter though? It's clearly a legally frought concept, and nobody actually believes in public domain itself as an ideal (as far as I know), its just seen as a means to an end, the end being a release of all "legal entanglement" upon the work. If that means is problematic, why not use a less problematic means? Specifically, there exist licenses that give everyone every possible right that they can be given without needing to invoke public domain at all, and that should be sufficient for anyone who doesn't want to retain their default rights, so why is public domain anything more than a legal dead-end? (ignoring of course that it's still relevant as the eventual end of copyright once someone's been dead for longer than Walt Disney)