Becuase you would not be entering your password into the browser, or a web site, you'd be entering your password to a seperate password manager, presumedly with

Becuase you would not be entering your password into the browser, or a web site, you'd be entering your password to a seperate password manager, presumedly with an OS-level dialog which would would be using the backend protocol to verify/hash against the origin domain and supply the right key.