Just because a motorist exits their vehicle doesn't mean that they are at a disadvantage. You have no idea what a motorist may be carrying inside their vehicle. It could be a steel pipe, a baseball bat, a tire iron, a cheater bar, a hammer, an axe, a machete, a knife etc. All of those are very effective weapons and even if you carry a pepper spray it would still be very hard to defend yourself against an armed attacker who is motivated and determined to hurt you.