Do you have proof of this claim? I go to bed and don't touch my phone for 6+ hours and Touch ID still works perfectly fine when I get up. The only time I need to enter my passcode is when my phone is restarted or my hands are particularly sweaty / dirty.
This happens to me all the time. My iPhone asked for my passcode when I don't use it for a certain period of time.
TouchID is flawless for me so I never use a passcode until I get a prompt