Because the frame number is unique and cannot be changed.

Frame number is the vehicle identification code of automobile products, which can be said to be the id number of each automobile product. Manufacturers who compile and label vehicle identification codes must file with the Standardization Institute of China Automotive Technology and Research Center at least one month before using the vehicle identification codes for the first time.

The frame number is not only on the body nameplate, but also on the door, firewall, central keel, underbody, hood, trunk lid and other objects. Although the nameplate can be replaced, the cost of replacing the car body is too high.