A thief flags you down, grabs your phone and makes you unlock it using your thumb.
A cop opens the cop car door, grabs your hand and unlocks your phone, or even easier, face unlock.
Granted, guns and torture are rather effective as well, but is anyone entirely against fingerprint unlocking?
Graphene allows for fingerprint and second factor pin unlock, which is what I use. I mostly do that for cops, though, since in the US you can be legally compelled to unlock your phone with biometrics but not pin.
Wouldn’t stop someone from torturing you to unlock your device, but that’s what a duress pin is for ;) (they may kill you once your phone wipes but at least they wouldn’t have your data)