Clean environs is just good werewolfing. Pollutants having their own spirits aside, they also cause disease, famine, death, and general misery, which bring Flesh and Spirit disasters. Consider Detroit: burning rivers used to be a seasonal occurrence, they've had outbreaks of Legionnaire's Disease, and quite a bit of corruption and malfeasance with water infrastructure. Pollution is destabilizing, and an unstable territory is bad for every pack.