Because the United States does not ration care. Other nations employing a socialized form of healthcare, by necessity, must ration care because for something like one's health, the demand will always be greater than the supply.
Bull Shit. I happen to live in a country with socialized healthcare and have never experienced "rationed healthcare". Don't fall for that right wing crap that was spread around. Most of it was outright lies.
Other than covering the costs, the Canadian gov't has essentially no say in treatments. The doctors decide. There isn''t a bureaucrat hanging over the doctors shoulder. There isn't any gov't red tape. I get sick, I go to the hospital, I get fixed, I go home. Oh, I do have to show my healthcare card and put a signature on a piece of paper. So I guess there is some red tape.
The trade off our taxes are slightly higher north of the border. However, I think that is a fair trade off to know that my neighbour, whose daughter had severe heart and kidney problems from birth, didn't have to worry about how they were going to afford to keep her alive.