Why was the Great Wall of China built only in the north?

China is a unique state that has been successfully hiding from curious Europeans and treacherous nomads for many centuries. Ancient China was located so that in the south its borders were protected by the deep rivers Yangtze and Yellow He. In the East, the country was protected by the Yellow Sea, and in the west – by the high and insurmountable mountains of the Himalayas. And only in the north, where numerous tribes of the Huns lived, there were no natural conservation objects. For this reason, the Chinese built the Great Wall only on the northern borders.