You’re confusing plagiarism for copyright infringement. Copyright infringement is what you’re describing. Technically, some of the most textbook severe cases of academic plagiarism don’t infringe copyright. Plagiarism is taking someone’s ideas without proper credit. In academic spaces, plagiarism is not usually a legal dispute, but instead a matter of integrity.

These AI plagiarise by nature, because they are incapable of saying which of the data in their training database was used in the creation of each of their works.