But fair use, as I understand it, is only about outputs, not inputs. (Licenses can apply to inputs.) A copyright violation occurs when one produces a work that infringes copyright. In this case, Google made digital copies of the books and showed snippets of the books to website visitors. Fair use refers to cases where producing that work is nevertheless legal.

The only analogy I can see is that copying the code internally to use in CoPilot training could be a violation of copyright (like how backing up your own MP3s is a violation of copyright?), but the licenses on these public repositories probably already allow that...