[surteen]

Because it's a PIN protecting a certificate stored on the device. Even if you know the PIN but don't have access to the device, you can't use it.

[toomuchtodo]

And the pin is the same functionality as activating a hardware authenticator like a Yubikey.

[stouset]

… which have historically yielded credentials at any touch, without a need for a PIN, fingerprint, or face scan.