I think its because Starvation is pretty potent once you get all the 'DoT' spells onto someone's food production...

If a province has zero food, it will enter into a state of starvation. While a province is starving, its population (peasants, military units and thieves) will die off at a rate proportional to the food deficit (this also includes armies away from home). Wizards are not affected. This rate is capped at 5% and will continue until the province has a value for food greater than 0.
Pretty comparable to overpopulation over 115%