Forced economic arrangements.
You can't have universal coverage unless you use the force of government to make people do things they don't want to.
It's perfectly reasonable for the government to force individuals to do things when the failure to do them has negative consequences on others.
That's why it's perfectly reasonable for the government to force you to buy auto insurance, keep your front yard in good condition, mow your lawn and rake your leaves, sweep the snow of the sidewalk in front of your home or business, etc.
People who choose not to buy health insurance take a significant risk of becoming wards of the state. If they get seriously sick, they can just go to an emergency room and stick the rest of us with the tab if they can't afford to pay it. It is thus perfectly reasonable for the government to require some minimum level of catastrophic coverage so as to prevent such freeloading.
It also has the added benefit of reducing adverse selection costs.