Because many Asian countries in that area have little or no pollution laws. Like Thailand, if you ever went to Bangkok where a lot of the factories are, you will have to wear a mask out in public. Most people who ride motorcycles or "Tuktuk" cars with no windows will be wearing a surgical mask or a filter mask. Even the Police wear them. Automobiles have no emission laws in Thailand, so they can run them as dirty as they want to be. I assume that Burma, India, Pakistand, and others all lack the type of pollution laws that the US has.

Even Godzilla couldn't stand up to it, and would choke on it and eventually die.