Demanding a password introduces more error and more room for evasion than a finger, which as I said is about the same as getting the phone in the first place. You are right that in some, maybe even most cases, it may not make a difference. But when time is of the essence, additional obstacles are often simply avoided.

You also might ask who is sticking you up. For example, I believe there is fourth amendment literature re government officials that have gotten away with using an arrested persons biometrics to unlock a phone, in a manner in which compelling the release of a password would be illegal. Put another way, I can simply grab your finger or put your phone in front of your face, whereas beating you until you surrender your password is a lot harder to accomplish without creating additional consequences.