What is stopping people from getting together and forming their own "universal health care" group? There must be millions who are in favor of it? Get 100 million people together, and offer health care to each other. What's stopping you?
Some of them would have to put a lot of money at risk. When they do that, they usually want something in return. Well this is how corporations were invented. And those are regulated.
Typically the State medical device licensing boards will stop you. Try this: get 1000 families to chip in for an MRI and techs to run it for the benefit of the 1000 and their families. When you apply for State permit to turn it on, that board will look at competition in the area and not allow it. The rules don't allow too much competition to drive down prices, so only the mega-corps typically can play the game.