Biometrics like TouchID work fine for authentication, but they don't work for encryption. Encryption requires a secret, and you can't really call your biometric

Biometrics like TouchID work fine for authentication, but they don't work for encryption. Encryption requires a secret, and you can't really call your biometric features a secret (even besides that it probably won't be of high enough entropy and that you wouldn't be able to have more than one set). This is why iPhones always ask for your password when you restart your phone -- it's not just a security feature, it actually needs your password in order to decrypt the phone data.