With my insurance, I have to pay extra because I smoke.
However in my line of work I see people who are on Medicaid and don't pay a dime for their coverage are constantly abusing drugs, but they are not punished in any way for this.
Actually, the tax code does already penalise people with poor health habits.
But it punishes them at the point of consumption - when they are actually doing the 'wrong thing' by following unhealthy behaviour. It doesn't penalise or discourage them at the point when they do the right thing by seeking medical help when it is needed.
US smokers are taxed when they buy packs, at the state, federal and sometimes municipal levels; and there are similar liquor taxes, etc. These all are applied at the point the health-damaging behaviour is initiated, and there's plentiful evidence from many worldwide studies that, depending on how these taxes are applied, they do in fact reduce things like smoking rates, particularly among younger people. Here's one such example among many from 2011 (this is disputed by the tobacco industry and its affiliated researchers and think-tanks, obviously, but the evidence is strong). For illegal drugs, obviously they're illegal - mere ownership is penalised (in some states, very strongly).
If there was some governmental penalty and disincentive at the point a person with unhealthy habits identified possible health problems and sought treatment, you'd be penalising and disincentivising the thing they did right. Almost all medical conditions, and especially cancer, can be treated more easily, safely and cheaply when they are caught early. In particular, emergency treatment is colossally expensive, and hospitals tend to bill people on Medicaid higher. Anything that makes unhealthy people more likely to delay seeing a doctor will wind up increasing the costs of their treatment.
So, when people's health care is taxpayer-funded, you get best value for the taxpayer (and best health outcomes) by:
There are other approaches to disincentivise unhealthy behaviour that don't counter-productively increase total costs. For example, in the UK where all health care is free unless an individual chooses to upgrade, some regional health trusts have begun withdrawing non-essential non-urgent treatments such as IVF to smokers and others. It's very controversial, and it's too early to say what impacts it has, but it's unlikely to result in higher fees down the line.
This does leave the question of, why are non-medicare Americans who have unhealthy habits, like the asker, penalised for a second time at the point where they do the right thing in seeking medical attention when they show signs of being unwell (or in preparing for such an eventuality with insurance), when they've already paid once through taxes?
The short answer is, it's financial, and nothing to do with punishment or blame or morals. When health is treated as a marketplace and health-providers are profit-making, anyone at a higher risk of needing expensive treatment is a greater financial risk. If it's legally allowed, their premiums will be higher, regardless of whether it's "their fault" (smokers) or "not their fault" (pre-existing / genetic conditions).
As for the pros and cons of structuring a system like this - that's a separate question.
Because there's no realistic way to punish them. You can either:
Take away their medical services access.
Obviously, that isn't ever going to fly in the modern welfare (or social safety) obsessed society.
Punish them materially.
Obviously, if they are on medicaid, they don't really have any material wealth to take in punishment in the first place.
Punish them legally.
Throwing people in jail for poor life choices isn't exactly going to be a popular option with most people in the first place; and when we tried that (prostitution, drugs, or in USA, alcohol), it doesn't really work well. Plus, it's even more expensive anyway - you would have to medically treat the slackers while incarcerated.
Punish them socially.
Society used to very effectively use public shaming to that effect. The problem is three-fold:
First, public shaming no longer works in our extra-scaled-up society, compared to small village. You can't shun someone effectively in a city of 100K or 1M people. Second, many people like this simply don't care about public shaming. And third, modern Western societies shifted their mindset away from blaming people for their poor choices, labeling everyone a "victim" and finding excuses for why those bad choices were made. Public shaming is quite contrary to that life philosophy.
Because few people want to punish them.
The only people who get directly negatively affected by this are the taxpayers. There are fewer and fewer people who pay any federal taxes (at least in USA) of any meaningful size - at this point, <50% in USA - and those people have less and less political influence. And a large chunk of them bought into the whole welfare capitalism idea in the first place, since it largely doesn't exhibit major structural problems for decades and does make people feel good about themselves.