I am pretty sure if the authors were trying to license their works for this purpose we would just not use them at all; it is difficult to see under what circumstances they would stand to profit from this other than by suing people after the fact over it.

I think you could argue that authors could profit from their works being cited in an LLM response. It could drive sales of their works much like citations do on the web. The counter argument is that and LLM could give you the Clif Notes version of the work and thus taking away a portion of sales.

In a world where the options were to

1) pay the author,

2) implement guaranteed citation of the author any time the model gave an answer that was directly derivative, with an option to not do so if the summary was sufficiently vague, or

3) ignore the author's book completely as training data

we would all choose 3).

And the authors would probably be very happy that you did.