That's quite a convoluted scenario. But ok, I see your point.
So with your Touch ID - what happens if you're mowing the lawn, drop your iPhone and then as you reach down, chop off all your fingers? Whilst you're in hospital, amongst the long grass, a man who has inadvertendly found himself in your private garden, finds your phone and one of your fingers and... BAM! He's in your iPhone with access to all your stuff.
Your bank account is empty within minutes, your wife leaves you and you're homeless.
Not saying Touch ID is a bad thing, but I don't mind simply being careful to be aware where my phone is and not drop it and let others get to it. It's be sixteen years so far and I've not lost it yet.