Because there's no way the code is distributed properly according to any of the OSS licenses. In fact, it claims authorship with nonsense bylines saying the LLM wrote it.
National Law Review covered some of those nuances last year: https://natlawreview.com/article/federal-courts-issue-first-...
US Copyright Office has a substantial document discussing each of the four factors, and making it clear this is an unanswered question, and details of the particular case will decide which way courts go. It is a prepublication version, and it's over 100 pages, but it covers the issues well, citing arguments on all sides.
https://www.copyright.gov/ai/Copyright-and-Artificial-Intell...
What are you talking about? There is no distribution, only read access.
That said, FOSS licenses are non-exclusive. Regarding the original upthread topic of GitHub's copilot training, iirc GitHub's terms and conditions involve granting them a license in order to host your code. Depending what else is in those terms, they may have had the ability to use all hosted code for LLM training through that license, instead of the FOSS licensing on any given Open Source repo. But that would only apply to GitHub/Microsoft, not third party scrapers.