Why did 500,000 Qin Jun in Lingnan let the Qin Dynasty perish?

During the three-year war from 209 BC to 206 BC, 500,000 Qin Jun, who was guarding Lingnan, was indifferent to the demise of the Qin Dynasty. Why?

The whole land is king. The first emperor ruled the country by legalism, and the concept of "everything should be in all directions, in the center, saints should persist, and all directions should be effective" made Qin Shihuang take attacking the south as his own responsibility and expand his territory indefinitely. At the same time, conquering South Vietnam has strategic advantages. At that time, 600,000 had just conquered Chu, and now Hunan, Fujian and other places have all returned to the territory of Qin, forming a strategic pincer-like offensive against South Vietnam, so it is reasonable to recover South Vietnam south.

However, compared with the success of attacking Xiongnu in the north, the first war of conquering South ended in Qin Jun's crushing defeat, and even Tu Youyou, commander-in-chief of Qin Jun, died. Historically, South Vietnamese aborigines "get along with animals" and "don't want to be Lu Qin". This forced Qin Shihuang to readjust the strategy of conquering South Vietnam: slow and steady, heart-oriented, emigrating to the border and stationing for a long time. In 2 14 BC, Ren Tao and Zhao Tuo led the second expedition to the south, and the deceased Qin Fa, her husband and merchants were embedded in the army, which not only established a solid military stronghold for Qin Jun, but also greatly developed the Lingnan area, enabling Qin Jun to successfully capture the area and set up three counties. It was not until four years later that Qin Shihuang died in a sand dune, and the 500,000 troops that Qin conquered South Vietnam did not return to the north. History books do not record why the Qin Dynasty did not recall its headquarters in Qin Jun.

But obviously, this should be allowed by Qin Shihuang, and even we can boldly speculate that in order to completely conquer the land of South Vietnam, the first emperor may have a special imperial edict for Ren Tao and Zhao Tuo, in case that once Qin Jun left, Baiyue people reoccupied the three counties, resulting in hundreds of thousands of people killed in Qin Jun donating blood without compensation, which can be seen from Ren Tao's instructions to Zhao Tuo before his death. In 209 BC, an uprising broke out in Chen Sheng and Guangwu. As the supreme commander of South Vietnam, Ren Tao told Longchuan on his deathbed and ordered Zhao Tuo to "let his people rest and wait for the change of the governor.