Many people don't have much income but are quite healthy, easily able to go years without medical services (yes, in fact a great many people do). All they need is "catastrophic coverage", but that alone is illegal under ACA.

Likewise the rich. If you're earning millions per year, you don't need ACA-imposed "$50 co-pay" type coverage for common services totaling under $100,000/yr. (Listen to Rush Limbaugh rant about such issues: forcing him to buy ACA-approved health coverage is stupid; he could buy the hospital if need be.)

Comes down to marketplace & choice: it's my life, and my money, who are you to force me (under threat of violence from the state) to buy what you consider sufficient coverage? Let's discuss fixing systemic problems with narrowly targeted solutions, yes, but don't fine me $3000/yr for preferring to pay my own way out-of-pocket completely up to $10,000/yr.