The idea that AI-created music should just go into the public domain is I think the wrong kind of thinking. It is not simply that AI has no access to copyright, AI has no access to moral rights either. My understanding is that it didn't actually create anything.
Now if an artist uses an AI as part of their work, they are doing some creating, but the AI has no more role in the process than a set of speakers. No one extends their creative credits to their amp. Moog don't make music no matter how important their instrument was to the sound. If I make a random hole puncher and feed it's output into a player piano the machine isn't making art.