Why are there no Han people living in southern Xinjiang?

Southern Xinjiang has been a multi-ethnic and multi-religious area since ancient times. Since the Western Han Dynasty, it has become an inseparable part of China's unified multi-ethnic country. The "Silk Road" in China's history starts from Chang 'an, passes through Hexi Corridor, then passes through Xinjiang, and finally reaches Europe through Central Asia. Southern Xinjiang is a part of Xinjiang, located in the northwest of China, at the southern foot of Tianshan Mountain in Xinjiang. Southern Xinjiang has been a multi-ethnic community since ancient times. The arts and colorful customs of Han, Uygur, Tajik, Kirgiz and other ethnic groups constitute a humanistic landscape with strong national characteristics. Southern Xinjiang is a part of Xinjiang, located in the northwest of China, at the southern foot of Tianshan Mountain in Xinjiang. Southern Xinjiang has been a multi-ethnic community since ancient times. The arts and colorful customs of Han, Uygur, Tajik, Kirgiz and other ethnic groups constitute a humanistic landscape with strong national characteristics.