There's so much pollution. This is why smokers are more prone to colds and other diseases. Besides, according to the Environmental Protection Agency environmental tobacco smoke is the major polluter of indoor air.
People spend more time indoors than outdoors.
While car pollution is definitely a problem, our society has accepted much of it because of its redeeming use. There is no redeeming need for smoking. Indoor air pollution from tobacco smoke is often worse than outdoor pollution. This is an indoor air problem. You don't see too many people driving cars indoors.