Why does Xinjiang have a Corps but not Tibet?

The environment in Tibet is poor.

Although the two major basins in Xinjiang are covered with large areas of desert, due to the existence of the Altai Mountains, Tianshan Mountains, Kunlun Mountains, etc., a large amount of melted water from mountain ice and snow has resulted in a large number of oases distributed between the foothills and basins, which facilitates human survival and development. The average altitude of Tibet is over 4,000 meters, the air is thin, the land in most areas is barren, and the natural environment conditions are poor.

Xinjiang Uygur Autonomous Region, referred to as Xinjiang, is located in northwest China, in the hinterland of the Eurasian continent, with an area of ??1.6649 million square kilometers, accounting for approximately one-sixth of the country's total land area.