Your biometric measurements are essentially secrets. They work today because it's far too difficult for a thief to steal your device AND copy your biometrics at the same time. This makes them the most secure tokens we have in real world use, given the number of people with 0000 passcodes.
Eventually they may become easy to copy, then their utility as secrets will be gone.
Eventually they may become easy to copy, then their utility as secrets will be gone.