Digital computer-aided plagiarism is new ground for copyright. Google has successfully defended Google Books with the defense that it is searching an archive of legally purchased and licensed books for specific information without reproducing the entire work. It's the equivalent of visiting a physical library or bookstore and flipping through a book without actually purchasing it.
AI is something else entirely. It's more like a program that incorporates ALL of the text (training data) and alters it according to an algorithm. This has been a problem with news-crawling websites for a long time. They would download copywritten text, edit multiple sources together, or use an algorithm to replace common words, etc., then post it on their own ad (and often virus) filled sites. It seems like AI is just a more sophisticated version of that. In any case, I'm not a lawyer so who knows what the argument will be on one side or the other.