Why are some carcinogenic agents, like those found in cigarettes hard to regulate

Question

Why are some carcinogenic agents, like those found in cigarettes hard to regulate

Answer 1

Could it be that while a very large percentage of those who contract lung cancer inhale cigarette smoke, only a very small percentage of those who inhale cigarette smoke contract lung cancer?

Or , could it be that a very large percentage of those who fervently advocate the regulation of suspected carcinogens found in tobacco cigarettes also fervently advocate the deregulation of those same suspected carcinogens in marijuana cigarettes?