Yuan Tiangang is a fairy, why not give it to Li Xingyun?

As the maker and experimenter of the elixir, Yuan Tiangang lived forever because of the elixir, and it was precisely because of Yuan Tiangang's ability to live forever that Emperor Taizong later ordered him to form a secret organization dedicated to serving the royal family in the Tang Dynasty. This organization is a bad guy, and Yuan Tiangang, as the leader of this organization, has never been called a bad handsome. Then, as the producer of the elixir of life, why doesn't the bad handsome improve the elixir of life so that users don't have to pay the price of disfigurement, and then continue to refine it? I think there are two main reasons why bad coaches stop improving the elixir and continue refining it.

First, there is basically no obvious emperor since Emperor Taizong. Although Bad Men is a fictional cartoon story, some historical facts should be respected. For example, the emperor of the Tang Dynasty, looking back at history, has existed for nearly 300 years since the establishment of his own country. After the death of Emperor Taizong, the Tang Dynasty basically lost its elegance in the Zhenguan period. Even a few years after the death of Emperor Taizong, the land of the Tang Dynasty changed hands. After Tang Gaozong's death, the throne of the Tang Dynasty was actually taken away by his empress Wu Zetian. Later, only in the early days of the reign of Emperor Xuanzong of the Tang Dynasty did the Tang Dynasty restore some elegance during the Zhenguan period, but this prosperity did not last long. Emperor Xuanzong of the Tang Dynasty favored Yang Guifei and let An Lushan go, which led to the Anshi Rebellion. Since then, the Tang Dynasty has completely lost the scene of its heyday during the founding of the People's Republic of China.

Second, Yuan Tiangang deliberately failed to refine the elixir of life, whether according to the plot in Bad Men or according to unofficial history's records. During the reign of Emperor Taizong of Tang Dynasty, two magicians, Yuan Tiangang and Li, used divination to calculate the national fortune of Datang at the same time, and both of them calculated that Datang would perish after 300 years. After the two got this number, Li thought that they should follow the fate. After Datang existed for 300 years, let it disappear, but Yuan Tiangang didn't want it to be resigned. He wanted Datang to exist forever, but God's will was inviolable, so Yuan Tiangang came up with another way. Let Datang perish first, and then he created another Datang.

To sum up; Yuan Tiangang didn't improve the elixir for three hundred years, and the main reason for refining it again was that he didn't want to refine it at all. First, the emperors after Emperor Taizong had nothing to do, and second, he knew that the life span of the Tang Dynasty was only 300 years. Even if he refined the elixir for those mediocre emperors, it would not change the fate of the demise of the Tang Dynasty, so he chose to perish and then create another one. This is also the reason why Yuan Tiangang has not improved and refined the elixir for three hundred years.