If the average cost of a person's health insurance premium yearly is $5,000, and the average ER visit is $1,300, factoring in deductibles, you'd have to go to the emergency room 5+ times a year to break even. You're betting you'll get hurt bad enough to make back the money you're spending. Unless you're at risk for something like cancer or surgery, it just isn't financially smart for some people to buy insurance.
The problem isn't when you have to visit the ER for something minor, but when you get into an accident or you have a heart attack or stroke. It's going to cost you more than a $1,000 to treat that.