Throughout history the armies that pillaged a countryside often lost the support of the locals whose land they were pillaging, often to the point where they had to withdraw or change their strategy after incurring too much local backlash. In Civilization, an invading army really doesn't face any maluses associated with pillaging territories (and indeed, it is basically a meta at this point). Would it be more realistic if pillaging a city's hex increased the defensive strength of the city itself (representing citizens who either fled the pillaged land and reinforced the city center, of who had their resolve increased to fight the invader harder) or increased the loyalty pressure from the besieged city and nearby cities against the invader? Right now, a general strategy is to pillage a land completely, capture the city center and take a builder to repair all the damage. What this doesn't address is the resentment of the people who had their land's pillaged by the invader. It would make capturing cities more strategic (and realistic) if you had to choose between a 'no pillage' strategy that increased the chances of keeping the city once captured and a "pillage and burn" strategy where you were better off razing an angry city after you'd ruined its lands.