Actually, it's not that no one is named "Gui", but few people are named "Gui". For example, during the Jiajing period of Ming Dynasty, there was an assistant minister named Sun Gui. A famous professor of history in Beijing Normal University is Wang Juelin. At present, I know only these two people whose names have "Gui". I think few people are named "Gui" for the following reasons:
Qin Gui is one of the famous treacherous court officials in the history of China. Legend has it that during the Qianlong period, the top scholar Qin Jianquan (that is, Qin Dashi, whose name was Jian Quan) was a favorite pupil of the famous poet Yuan Mei. One day, Qin Jianquan went to visit the West Lake with his friends. When he arrived at Yue Fei's tomb, everyone saw Qin Gui kneeling in front of the tomb and couldn't help but make a poem about it. Some people found Qin Jianquan silent, so they deliberately grabbed him and wrote couplets on Qin Gui's knees. Although Qin Jianquan was happy, it was hard to refuse. When he was at a loss, Yuan Mei helped him say that "people were ashamed of their names after the Song Dynasty", and Qin Jianquan received "I went to the grave to be ashamed of my surname Qin", and with the help of Yuan Mei, he was relieved. After the Qin Dynasty, Jian Quan wrote a complete pair, which has been passed down to this day.
It can be seen from this story that since the Southern Song Dynasty, people hated Qin Gui and were even more ashamed to share the same name and surname with him. Therefore, few people named him "Qi".
Extended information:
Qin Gui (19-1155), whose name is Huizhi, was born in Huangzhou and his native place is Jiangning (now Nanjing, Jiangsu). In the early years of Southern Song Dynasty, he was a prime minister, a traitor, and a representative of the peace faction. He was one of the famous traitors in the history of China.
reference: Qin Gui _ Baidu Encyclopedia Wang Yulin _ Baidu Encyclopedia Qin Dashi _ Baidu Encyclopedia