You can understand why it happens. For millions of years while we evolved into what we are, we didn’t have a ready supply of food in a fridge or cupboard that we could just nip to. We might have not been successful with hunts, a rival tribe might have eaten and taken all the local growing fruit for themselves, we might be in the middle of Winter where nothing much is growing so what food we had (nuts, dried and smoked meat) might be only eaten every few days, a natural disaster like a flood could wipe out our territory, we might be stuck up a tree for a couple of days while a pride of lions is waiting below to eat us… so our bodies evolved to eat the waste from our own bodies to keep us alive.
Be interesting to see if more studies come out about this as there seems to be very little about it with regards to humans (how long we should fast for to hit the ideal for autophagy, whether we can consume anything at all while fasting…).