Because there's a bill. Here in Canada, we have universal single payer, and the hospitals are non-profit. They still bill you, or your insurer (usually the public insurer). Because the hospital has salaries to pay, and drugs to buy, and equipment to maintain.

It's a nice idea in theory, but if we simply provided healthcare to anyone who showed up at the hospital, we'd probably have to close the border with the USA or something because ... anyone in America that's sick could show up and get treated and we simply could not afford that. As you note, the world is a long way away from the basic standard of a humane civilization.