Most people who die from smoking don't die from cancer. You could easily reduce the risk of lung cancer from cigarettes, but that would place an enormous burden on the healthcare system, because then smokers would just die from more expensive conditions like emphysema.

If government required tobacco companies to limit the amount of radiation in their productions, cigarette taxes would need to go up to compensate. The real solution is just making the sales of cigarettes illegal, and then forcing people to buy loose tobacco and roll their own if they want to smoke.