WHY DO I NEED TO ENTER MY PASSWORD ON MY IPHONE INSTEAD OF USING MY THUMB WHEN IT RESTARTS?

Fully embracing becoming the Andy Rooney of ListApp
  1. What's different when your phone turns on?
  2. Do they want to make sure someone hasn't cut off my thumb and is using it to get access to my phone?
  3. Or they've just killed me and are holding up the phone to my cold, dead hand?
  4. Or perhaps if I use the exact wrong password, the phone will automatically contact my spy agency and tell them I've been burned?
  5. Literally no other explanations possible, but go ahead and try