The biggest problem imho is that we only have two states on our phones - locked and unlocked.

Ideally, I should be able to unlock the phone and take photos using just my fingerprint. In my case I would also like to be able to call, message, play games and similar. But to access the 2fa app, cryptoasset app or similar, I must further authenticate in a way that I only reveal parts of my secret ("Enter 3rd, 8th and 11th character of your password:"). The assumption here is that I will mostly authenticate in a private setting, but sometimes I might not have that luxury.