Because ancient times were feudal dynasties, the status of the emperor was supreme, and others could not surpass him in any way. If there were those who had the same surname as the emperor, they should be named after the emperor at that time. The emperor was shy.
In other words, the requirements of ancient emperors are not that they cannot have the same surname, but that they cannot have the same name. Because the emperor's status is noble, taboos must be avoided. For example, Emperor Yongzheng of the Qing Dynasty was named Yinzhen, and his brothers all had the same name. His name was Yin. Later, after he became the emperor, his brothers were all changed to Yun.
Surnames are not restricted by taboos, and the emperor’s surname is also called the national surname. There have been many times in Chinese history where emperors gave surnames to people. The more people with this national surname, the more noble they are, which can also show the influence of the royal family. And even taking Zhu Yuanzhang as an example, I have never heard of him asking people with the same surname as himself to change their surnames.
On the other hand, several members of Zhu Yuanzhang’s royal family have changed their surnames. For example, among the descendants of Emperor Jianwen, some said they would change their surname to He, while others said they would change their surname to Dun. Some of them changed their surname to Chen when Zhu Yuanzhang and Chen Youliang were in decline during the war. After Chen Youliang was defeated, they changed their surname to Tian. etc. Li Bai of the Tang Dynasty was naturally still surnamed Li, otherwise we would have used another name when studying.
In fact, in ancient times, it was not just emperors who had to avoid taboos. Anyone who was an official also had to avoid taboos. The names of her father and mother also had to avoid taboos. In Dream of Red Mansions, Lin Daiyu’s mother was named Jia Min. As long as Lin Daiyu saw Min She pronounces all the words as secret.
Sima Zhao because his name was Zhao, and Wang Zhaojun, one of the four beauties in ancient China, was named Zhao. In the Jin Dynasty, to avoid Sima Zhao's taboo, he called Wang Zhaojun Mingfei.
So, I think Emperor Guda’s request to avoid taboos also shows a sense of respect for the emperor.