Don't eat right? Healthy is expensive, processed is cheap. Let's be honest for $5 you can buy a couple cases of ramen and several boxes of mac 'n' cheese or a couple frozen family sized entrees. Horrible nutritionally speaking but it takes away the hunger pains for a few days. Also when you're coming home after your second job and the kids are starving it's a whole lot quicker to pop a plate full of pizza rolls in the microwave than try to cook up some of the shit in these healthy living cookbooks.
Don't get preventative care? Even with Medicaid you still have to take off time from work and when you boss says no, you have to choose between being sick and losing your job. Also finding a doctor that takes adult medicaid is a real pain in the ass, take it from someone who has had to do it. Once you find one who takes it they only seem to do what is minimally necessary to treat you. I remember getting one side of my mouth taken care of at the dentist and then waiting until the new fiscal year started to get the other half done. One more thing: getting medication for chronic pain on Medicaid can be an epic battle.
Homeless? When I lived in Missouri there was a woman living on the streets who told me she did it by choice because she couldn't stand being enclosed in a room. That doesn't mean that all or even most homeless people are there by choice. From what I saw volunteering at a shelter, opening up access to mental health treatment would go a long way toward dealing with the homelessness problem in America.