Why lock a seed phrase with fingerprint or biometrics?

I want to get the 12 words, but it asks for either fingerprint or key number. This is general in other wallets, but why asking for fingerprints of the apps if the wallet is supposed to be anonymous??
Then I want to enter the key number, but in the app, there is no tab or access to set up this key number; how to set up the key number?

Imagine that you lost your phone. Someone can open the AlphaWallet app and reveal your seed phrase. Your funds will be at risk. Someone can clear your wallet out in a minute.

Your fingerprint or any other form of Biometric authentication is used to unlock your mobile device Secure Enclave. AlphaWallet is able to use the key from your mobile device Secure Enclave to decrypt your wallet key; then, you can use your wallet key to sign a transaction.

fingerprint alphawallet

Your fingerprint or any other forms of Biometric authentications is with your mobile device, stored and controlled by your mobile device, which is nothing to do with “ anonymous”.

Same as Biometric authentication, your PIN (key number) is used to unlock your mobile device Secure Enclave. It is with your mobile device, stored and controlled by your mobile device.

So the setup of PIN or Biometric authentication is on your mobile device.