Because the consequences after crossing are:
You can't adapt to ancient life at all. Become a beggar or starve to death. Which beggar do you think will go down in history? Don't tell me Hong Qigong is okay.
If you only have RMB, US dollars or future money, how can you live without a penny? At that time, you may become a tenant or a worker. Have you ever seen a tenant farmer or coolie who can go down in history? Don't tell me about Wei Xiaobao.
You know nothing about ancient prose, ancient living habits and ancient kings. Probably homeless because he was forbidden to go to the streets at night, and was arrested and beaten to death by officers and men. Don't tell me, you have to go through the Ming Dynasty to become a ZhangHaoGu who dares to rampage on the chessboard street.
If you encounter troubled times. Go and see "1942". If you can get into Chang 'an alive, you can.
So playing time travel is a narrow escape. Why is there a record?