Cassette Tapes and Private Copying Levy.
https://en.wikipedia.org/wiki/Private_copying_levy
Governments didn't ban tapes but taxed them and fed the proceeds back into the royalty system. An equivalent for books might be an LLM tax funding a negative tax rate for sold books e.g. earn $5 and the gov tops it up. Can't imagine how to ensure it was fair though.
Alternatively, might be an interesting math problem to calculate royalties for the training data used in each user request!
IMHO, a better example would be the AI generated summaries provided by Google. Often these summaries have sufficient information and detail that people do not read the source article. The authors aren't getting paid (perhaps through on-page ads, which are not viewed) and then go out of business.
This strikes me as a good fit for the tax-on-cassette metaphor.
Just as duplicating a fragment can be legal, duplicating any fragment on demand is not. Rephrasing a passage might be legal, but rephrasing any passage on demand might not.