Because the roof is a structural member.

The following is the introduction of major accident vehicles and accident vehicles: 1. Major accident vehicles: the top side beam, bottom side beam, rear fender, rear trunk and body frame of major accident vehicles may be deformed, or even have serious sheet metal repair or even cutting, splicing and welding. The engine and gearbox of vehicles in major accidents are generally overhauled, and even the whole power system will be replaced in serious accidents. 2. Accident car: The damage of the accident car is usually relatively small, and generally only the damage of the exterior cover exists, so the vehicle structure will not have much problem.