Most people will be using passkeys stored by Google or Apple's password manager services, in which case the device is an authenticator for the password manager,

Most people will be using passkeys stored by Google or Apple's password manager services, in which case the device is an authenticator for the password manager, not the passkey. I think GP is saying they would trust password managers with passkeys less than with credentials because passkeys won't be usable without access to the password manager, and will be difficult-to-impossible to recover and to move between services.