From lokedhs’ “There is much truth in what you say”:
The problem with fingerprints is that it’s inherently a very insecure way of authentication for two reasons:
Firstly, you can’t change it if it leaks out. A password or a credit card number can be easily changed and the damage minimised in case of an information leak. Doing this with a fingerprint is much harder.
Secondly, the fingerprint is very hard to keep secret. Your body has this annoying ability to leave copies of your identification token all over the place, very easy for anyone to pick up.