When airplanes refuel, one must always apply an earthing, why is this not necessary for cars

Answer

it must (is regulated) for airplanes and actually it should be just as good for cars. But drivers are much more undisciplined than pilots and it is impossible to oblige them.

Fuel for propeller engines is AVGAS100, which is almost identical to “super gasoline”. Equally flammable.
Jet fuel is kerosene, a type of paraffin, and much less flammable than gasoline.