And there's the problem that if the PIN or worse a biometric version of this becomes remotely well known you've now created an incentive for a car thief to kidnap people even if they only want the car.

Or anything else you can't easily transfer. I can't help but point at passkeys in particular (or 2FA in general).

A variant of this is the well-known scene from a previous century's movie involving extracting an eye to bypass retinal scanner.