You can't grant permission for something you don't own. Uploading a copy of a GPLed work to GitHub does not grant GitHub permission to ignore the GPL. (It might grant GitHub permission to ignore your copyrights in that work, maybe, though it seems like a stretch to argue that "run Github's services" includes "give other people derivative works of all your code"; arguably that ought to be too broad for a contract of adhesion. There's case law about what you can and can't do in a unilaterally imposed contract such as a ToS; a ToS can't say "you owe us $100 if you browse more than twelve pages" either, and codebases can be worth far more than that.)

If GitHub started saying "one of our services is to give people access to copies of your code with the licenses and copyright notices removed", the GitHub ToS wouldn't suddenly make it acceptable to run that "service".

But I agree with part of your underlying point. All AI models should respect Open Source licenses. It's a problem if some try to work around that.