A helmet in a car would limit visibility and movement and is completely impractical, not to mention mildly pointless.
On a bike you are exposed. In a car, you are not. On a bike you travel around 30km average. In a car, up to 100km average.
On a bike you are exposed. In a car, you are not. On a bike you travel around 30km average. In a car, up to 100km average.
When travelling at 100km with no seatbelt (legal in many areas), in a collision, you become exposed rather suddenly.