The reasons of each emperor's father are different, and the separatist regime in the buffer region is one of the most important reasons. But this alone cannot explain why there were so many emperors in the Tang Dynasty. It was only in the late Tang Dynasty that the buffer region dared to leave the central government. If we want to fully understand the Tang Dynasty, we must talk about Buddhism, saying that not talking about Buddhism in the Tang Dynasty is tantamount to smoking without ignition. So let's talk about Buddhism first. Buddhism is a foreign religion, but the emperor of the Tang Dynasty admired it very much, and the service of Buddhism was very prosperous. The whole people pay a lot of money to worship Buddha, which affects the social and economic development and causes the dispute between Confucianism and Buddhism.
Through the emperor's attitude towards Buddhism, the emperor of the Tang Dynasty was generally willing to accept foreign things and was not closed. The society in the Tang Dynasty was relatively open and inclusive, with social prosperity and economic prosperity. This is also an important reason why the 289-year history of the Tang Dynasty can be collectively called "the prosperous Tang Dynasty". Of course, during the revival of Huichang in Tang Wuzong, there was also a period of "Huichang destroyed Buddhism", but its purpose was to expand government tax revenue and consolidate power, which was only an episode. Because in the Tang Xuanzong period ruled by Dazhong, incense was very prosperous. It is precisely because of the obsession with religion that six emperors appeared in just over two hundred years.
The Tang Dynasty was a relatively existential dynasty in ancient China. It was really surprising and puzzling that there were so many emperors.