"supposed" is doing a lot of heavy-lifting here. According to who? The FIDO2 or Webauthn standards? Or in a perfect world?

FIDO 1.0 started as two different standards: UAF and U2F. U2F was for USB keys used as second factors (so almost always stored in a TPM-like chip and device-bound, but not provided by your platform and there could be multiple of them). UAF were either provided by your platform or by any software and there was no requirement for them to be stored in TPM. Back in the day, very few platform had any FIDO support built-in, so in practice UAF was always done in software (usually based on whatever biometrics/TPM the hardware provided).

So competing options were the default for early FIDO, getting a default platform option is something that came later.

The anti-phising benefits are still very much there even if you sync them to pw manager. Yes it introduces single point of failure (pw manager), but at the same time you no longer need to go reset all your passwords to every service you use if you happen to lose that device. Tradeoffs.

> They are supposed to be mathematically non-exportable, device-bound.

Which would make the whole scheme unworkable (at least for me).

Yeah - and as a user, I don't want my device manufacturer to have that level of influence or control over the authentication that I use for unrelated services.