US law enforcement is allowed to take fingerprints, which can then be used to unlock the device. Somewhere less friendly may just compel you to put your finger on the device
Your password is, in a weird US Constitutional sense, speech, and your 5th Amendment right not to be forced to self-incriminate protects you. Your fingerprint is not speech, and not protected in the same fashion.
(Once more for the folks in the back: fingerprints are usernames. Passwords are things you can rotate.)
Most other countries probably feel similarly, or they don't have anything like the 5th amendment. In places without something like the 5th amendment, you can choose to lie about your password, do it enough times, the device will reset and erase everything(assuming you set that up). One can not lie about their fingerprints.
Of course in places without something like the 5th, and you lie a few times, your death may find you quite quickly, there is at the very least an option... With a fingerprint, no options. Have a picture of your finger and game over.