Why can only the emperor know the Taiyi?

The reason why only the emperor can know the number of Taiyi gods is because it is a study of the emperor. First of all, the numerology of Taiyi God is a technique specially used to predict the national luck in ancient times. It is the study of emperors, which was only mastered by the palace in ancient times. Second, Qimen, Taiyi and Liu Ren are the learning of ancient san huang, which is called advanced prediction by modern people. This answer is for reference only. Don't be blindly superstitious.