You do realize that the median income monthly income is $277USD/month, right? A/C is a luxury for most. And even if builders put A/C in, many don't have the money to spend on electricity to run it.

Hell, when I lived in Singapore (3 degree from the equator), most homes had A/C, but many, many people never used it because the electricity was something they didn't want to spend their money on.

People have been living in that region for thousands of years, of which only the last 50 years has A/C been an option.