You're missing the bigger picture[1]:

  Numerous questions of law or fact common to each Class arise from Defendants’ conduct:
    whether ChatGPT itself is an infringing derivative work based on Plaintiffs’ copyrighted books;
    whether the text outputs of ChatGPT are infringing derivative works based on Plaintiffs’ copyrighted books;

It's not a simple case of "you used our copyrighted materials", it's "you're infringing on our copyright by producing works derived from materials that you used."

1. https://llmlitigation.com/pdf/03223/tremblay-openai-complain...