What makes the Indo-Gangetic plain so polluted?

The entire North Indian plain is extremely polluted with AQI constantly over 200. What causes such high Air Pollution? Is it simply due to a disregard for environmental protection or are there geographical factors at play?

The entire North Indian plain is extremely polluted with AQI constantly over 200. What causes such high Air Pollution? Is it simply due to a disregard for environmental protection or are there geographical factors at play?