One of the claims is that the book corpora weren't even sourced legally. It is harder to make a fair use claim if the copy the model was trained on was pirated

One of the claims is that the book corpora weren't even sourced legally. It is harder to make a fair use claim if the copy the model was trained on was pirated to begin with. Contemporary in-copyright ebooks are a bit different in this regard than images found on the public web.