because it is not the governments job to dictate people's lives. The result of smokers is a net benefit to the country, in terms of real tangible dollars. The intangible costs (which in this context is loss of life, yes they are putting a price on people, which is ridiculous in and of itself) is between the smokers and their family and friends. They are not burdened by anyone because they are intangible. You seem to have a shit understanding of taxes if you don't see that smokers are covering their own costs.
We also pay to treat those who are born with genetic illnesses, who work in coal mines, who drive dangerously, who eat unhealthily, who don't exercise, etc., but unlike them smokers do actually pay for the added cost to the system, many times over.