Because the car has headrests, safety belts, eight airbags, roll-reinforced occupant cage, reinforced door panels, crumple zones front and rear, reinforced tranny valley to slide the engine under the car instead of through it and four wheels - just in case I make a 4rse of myself and zone out on what I am listening to instead of what I am doing - driving. Or when I do not hear that semi with the bad tire right next to me. I have exactly none of that on the bike. Neither am I wearing earphones, blasting away inside a helmet when I am in the car.