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?
If you don’t have time to quickly disable biometrics (lockdown mode) before the cops grab it, you wouldn’t have time to turn it off either. A phone in AFU mode is very easily cracked with those forensic devices.
And they could just beat you for the password either way, given the current political atmosphere.