It's a combination of things. Ketosis does play a role, but the brain and gut work together to regulate hunger. The gut can stimulate hunger signals when empty and signal satiety when full, helping to regulate energy and metabolism in the body. There are more vagus nerves traveling from stomach-to-brain than brain-to-stomach, hence the term 'second brain' and 'gut feeling'.
The studies on hunger pangs seem limited; of the primary hormones involved in hunger is ghrelin, often called the "hunger hormone," which is produced in the stomach and signals the brain to increase appetite. However, ghrelin levels can rise even when you ignore your hunger, leading to increased hunger over time, but this does not mean that the feeling of hunger will persist indefinitely without any change in these hormonal signals.
Why? Perhaps our stomach can disassociate much like ours brain, especially when "needs" are not being met. It would serve us poorly as hunter-gatherers to be too hangry or cramped up when we go through a period of fasting/famine.
