Why this restriction on public-facing code? Are you OK with Copilot being used for "private"/closed source code? I get that it would be less likely to be noticed if the code is not published, but (if I understand right) is even worse for license reasons.
I have lower expectations of the rigor with which companies police their internal codebases, though. Seeing Copilot banned for internal use too is a pleasant surprise. Companies tend to be a lot more "liberal" in what kind of legal liabilities they accept for their internal tooling in my experience.