> I find it hard to believe that an organisation with GitHub's expertise and resources haven't analysed (and got comfortable with) the legal issues associated with the use of GPL / AGPL software to train CoPilot

Almost certainly. But what people tend to forget is that "working out the correct legal interpretation" isn't actually the job of a lawyer; it's the job of a judge. The job of a lawyer is to devise a legal strategy that works for the client.

In practice that will quite often mean "yes, this is illegal, but we will publicly claim that it's legal and ride the wave, and the consequences will cost us less than we can profit off it".

Even if it's not explicitly stated like that and couched in vague "legal risk" handwaving, the lawyer ultimately works for their client and that's who their allegiance is to, not to the law.