Why did humans lost their hair or fur on body ???

 Unlike other animals, humans are evolved to have a lot more sweat glands.

Instead of panting and hiding in the shade, our ancestors could cool down by sweating.

But for sweating to work well, body needed less hair to trap the heat and moisture.

This change led to a new way of hunting.  Here humans chase animals over long distances until the prey is collapsed from exhaustion in the heat.

By losing their fur, early humans gained an advantage. With less hair, they could effectively control their body temperature and had greater stamina.

In the hot climates, being less hairy isn't a drawback but it is a survival skill.