There are a large number of people with undiagnosed conditions due to factors beyond their control. You can incentive until the cows come home but magical thinking that "healthy diet" and "exercise" will cure everything is just that -- magical thinking. Subacute infections, auto-immune diseases, un- and under-treated mental illness are just a few of the conditions that will NOT respond to magical thinking. To punish people who are already ill on top of their illness is not a productive thing to do.
Even worse, with the very high and climbing cost of health "insurance" and copays and deductibles, very few of these people have a prayer of getting properly diagnosed and treated, in the few cases where there is effective treatment available.