> Every device is supposed to have its own unique private key, stored in TPM, released only when passing the user challenge (biometrics or pin, or a yubikey).

This is a misconception. A particular service can choose to enforce those class of passkeys, but most don't need that and shouldn't.

Passkeys are primarily meant to replace passwords and be hard (but not necessarily impossible) to exfiltrate.

The key difference is during normal usage you don't have to type the secret in anywhere, it's strictly asymmetric, so a unwitting user is far less likely to get fooled into accidentally leaking the actual credential.