I mean, no one ever said it was a good design.

But the original FIDO2 standard wasn't made with consumers in mind in the first place, it was driven by enterprises that wanted high-assurance security. It works in that environment because, well, a big IT department controls it, can support the employees, and you can mandate and control its use.

It was just sort of haphazardly shoehorned onto general users/consumers, prematurely IMO, via synced credentials as a compromise instead of coming up with something better.