Ask HN: Why even offer Touch ID if it wont unlock my iPhone?

This may be a very naive question. But whats the point of offering this feature if it simply cant unlock my phone?

background, I quickly reset my pswd last night + created a touch ID. But for some reason its not reading it the simple passcode ( i think it has to do with my new replacement glass that somehow mis-identified ( 2x! ) one of the passcode numbers I entered.

So I'm thinking so what right?! I have my unique finger print..right? NOPE sorry. You will need to restore the phone.

I would assume the unique touch ID would suffice as a unique secure measure and have that suffice/prioritized over a simple 6-digit code that can be easily seen entered by an 8 yr old child.