One reason would be exhaust fumes may enter the cabin area.
They may become unsafe to drive due to rust weakening parts of the car.
safety hazard
Reflective tape is not illegal to use on cars, as long as it is applied in accordance with local regulations and does not obstruct the driver's view or create a safety hazard.
A "safety hazard" is something that could cause a person to be injured or killed.
A step is considered a safety hazard if it is higher than 8 inches.
safety hazard: causes external harm (broken leg, sprained wrist) health hazard: causes disease. EX. Safety hazard is like not smoking around certain chemical carrying equipment (ie storage tanks) health hazard is not smoking in restaurants or other public areas.
harmful
Depends on the climate they kept in.
A loose valve stem in your car's tire can be a safety hazard.
to children
danger, risk, hazard
The salt and the water will erode the metal