All the corpses polluting the place. It's a huge problem, they ruin the air, turn the water non potable, look ugly as a dead asshole. Once the oil flow stops, fuel will become too valuable to use it in excavators to dig mass graves. Corpses will just rot there where they were killed. IWGY will eat some of them, but we're talking about thousands of people every day. Just imagine the stink and the consequences.