I think sometimes people refuse help because of the sanctimonious, judgmental, or otherwise unhelpful manner in which said help is provided.
It's one thing to educate someone about healthier habits.. it's another to attempt to shame or demonize them into assuming said habits.
We can't force people to abstain from risky behaviors. Likewise, I think it's important to remember before pointing the judgment finger at someone who's engaging in a behavior we find to be reckless, stupid, etc. that, in all likelihood, that person could just as easily be pointing their finger at us for something we do.
I once watched a morbidly obese middle-aged woman (in the process of consuming two Whoppers, a large fry, a massive soda, and a slice of processed chocolate cream pie) self-righteously condemn some employees who were smoking in front of the BK. "Ugh.. dis-gusting. Look at them, sitting out there sucking on their cancer sticks. Why on earth anyone would smoke is beyond me! They're killing themselves, and for what?"
She kept going on and on, and it was all I could do not to tell her to go have a look in the mirror.. 'cause if she keeps it up, she's going to be dropping from a coronary LONG before that kid gets lung cancer.
We all have our vices. I still say that's no excuse for denying medical care.