Earlier you gave the example of Facebook harvesting people's phone numbers. That's not just data that's information. But a Yubikey doesn't know your phone number, how much you weigh, where you live, what type of beer you drink... no information at all.
The genius thing about the FIDO Security Key design is figuring out how to make "Are you still you?" a question we can answer. Notice that it can't answer a question like "Who is this?". Your Yubikey has no idea that you're o8r3oFTZPE. But it does know it is still itself and it can prove that when prompted to do so.
And you might think, "Aha, but it can track me". Nope. It's a passive object unless activated, and it also doesn't have any coherent identity of its own, so sites can't even compare notes on who enrolled to discover that the same Yubikey was used. Your Yubikey can tell when it's being asked if it is still itself, but it needs a secret to do that and nobody else has the secret. All they can do is ask that narrow question, "Are you still you?".
Which of course is very narrowly the exact authentication problem we wanted to solve.