Have you ever read GitHub's conditions to know whether they also have the right to use your code that way, no matter how you decide to license it? I feel that you are overly focused on the legal part here, which I'm sure was handled by Microsoft's lawyers. I'm more interested in the question of principle.
No matter what the terms of use at SO say, anyone can give you an answer that is a copy of some code they don't own. You may consider that immoral, but I don't, not at the scope SO is used for. In addition, the vast majority of cases at SO and Copilot are not about complex functions being stolen, it's about some dumb code you would have found in 2 minutes of googling. What I'm trying to argue here is that if we are all cool with SO and think it's useful, there is no fundamental difference here. We never cared too much about licenses for boilerplate code, and I think we shouldn't start now.