Copyright as far as I understand is focused on wholesale reproduction/distribution of works, rather than using material for generation of new works.

If something is available without contractual restriction it is available to all. Whether it's me reading a book, or a LLM reading a book, both could be considered the same.

Where the law might have something to say is around the output of said trained models, this might be interesting to see given the potential of small-scale outputs. i.e. If I output something to a small number of people, how does one detect/report that level of infringement. Does the `potential` of infringement start to matter.