One reason why people have historically had trouble suing tobacco companies is that non-smokers also get lung cancer. While we can say for sure that smoking makes it more likely you will get lung cancer, it's generally impossible to say any one person's lung cancer was caused by smoking. This is in contrast to say, someone who injures themselves climbing, where it is definitely 100% on them.

The real answer of course is that you're paying for it either way. Insured people pay absurdly over the odds to offset the amount of money lost on people who accrue medical debt and can't afford to pay it off.