The underlying problem is that "meaning" in the ordinary sense still includes plenty of copyrightable elements. If you point a typical LLM program at some arbitrary text and tell it to "rephrase" that, you'll generally end up with a very close paraphrase that still leaves intact to a huge extent the "structure, sequence and organization" (in a loose sense) of the original. So it turns out that you're still in breach of copyright. All you're allowed to use when starting from a single copywritten text is the ideas and facts in their very barest sense.