Why does "Touch ID" require Passcode ON ?

I thought Touch ID was developed as a way (among other features) to not have to use a Passcode to unlock the lock screen.

If I enable "Apple Pay" for Touch ID, Passcode is slid to ON for unlocking.

Shouldn't it be Either/Or or both, rather than both all the time?

I want to just slide the toggle to unlock the phone, but still have Apple Pay enabled for Passbook.