Wet bulb temperature is a combination of humidity and temperature.

Wet bulb temperature of 35C means your body physically cannot get rid of heat and you WILL die, rather quickly, even in shade. There is no escape unless you have ability to control humidity (ie. remove some humidity from the air).

Up until recently we did not have situations on earth where wet bulb temperature would reach 35C. Even in the most hot places the air would be dry enough to bring wet bulb temperature down under 35C meaning, things can cool below human body temperature.

The issue is that a lot of people in hot places simply do not have the means to control their climate in their houses, assuming they have any.