The GPL only gives you additional permissions relative to what you would have by default. The books included in that suit were more strongly restricted, since there was no license at all.
There are certainly some interesting additional conditions the GPL creates by taking the license away if you violate certain clauses. Regardless, the interesting part of this is that this looks different from the user's point of view and Microsoft's. Sure, 5 lines out of 10,000 is probably fair use. For Microsoft, their system is using the whole code base and copying it a few lines at a time to different people, eventually adding up to potentially lots more than fair use.
The question on this one will be about the difference between Microsoft/Github's product and a programmer using copilot's code:
"If I feed the entire code base to a machine, and it copies small snippets to different people, do we add the copies up, or just look at the final product?"
> Why don't book publishers use a license that forbids fair use?
They couldn't do it with a license, which only imposes conditions for the license to be valid. Fair use applies even if the copier has no license at all.
Potentially they could do it with a contract. A license is not a contract and imposes no covenants on the parties.
https://philzimmermann.com/EN/essays/BookPreface.html