if they did, (just about) everyone would pay more and if they did they would have to determine if the discounted individuals were exercising as much as needed to be healthy.

Insurance is a fund paid for by everyone for the remote chance of an unexpected event. Most people live to a ripe old age, in spite of their poor health habits. Only 4% of deaths are from accidents and half of those are from motor vehicles. The vast majority of people reach age expectancy and just because you may be healthy now,it doesn't mean you won't get sick later.

You never know, insurance helps and it helps even better if everyone chips in. If you're confident on your chances of living long, go without. Chances are, you'll be fine, but if you're not, it'd be a bummer.