"They" cant tell us because nobody knows. Chances are, it'll always be impossible to know. It doesnt matter that much though, whichever answer it is, its gonna be too weird to wrap our heads around. That's already the case with a lot of physics we do somewhat understand.

I think the question there in terms of "absolute" is that the CMB is "special" in the sense of being the most distant observable "object", and thus is kind of "absolute" in the sense that its the most encompassing of all possible frames. I.e. all of the rest of the observable universe is within it. Kinda like a skybox in a video game.

What's the link for gps tagged humans?