Because, it is believed that first humans lived there.

East Africa - is coinsidered the cradle of humankind.

South Africa is where the 'Cradle of Humankind' is located.

The Cradle of Humankind (as a part of the Fossil Hominid Sites of South Africa) is a World Heritage site under criteria iii and vi. Found at the site were specimens dating back 3.5 million years and threw light on the origins and evolution of mankind. These sites are also situated in areas that allowed for the conservation of these fossils and the site is a vast reserve of scientific data universal scope and incredible potential. These sites conclusively proved that africa is the cradle of humankind.

Olduvai Gorge is known as the cradle of humankind because it has provided some of the oldest evidence of human evolution, including hominid fossils and stone tools. The gorge's archaeological sites have helped scientists understand the early stages of human evolution and behavior.