Lots of reasons for healthcare to cost more in the US.
More people making terrible life choices. A more sue-happy environment in which doctors need to get paid more, and also in which doctors over-authorize the kitchen sink for relatively minor things (CT scans for everyone!). A hospital price structure that is similar to going into a really fancy restaurant: a list of things you want, no costs listed anywhere; the same thing can be 3x the price three miles away. Private insurance takes a slice, of course. Bills that are way too high because the hospital expects everyone to only pay a fraction, either due to insurance agreements, or asking the hospital for a break, or just not paying. Our doctors almost certainly take home more pay after all costs too, which is a good thing IMO. We also don't cap the costs of treatments (drugs etc), largely because the US is often the source of many of the drugs in the first place (politics.) And so on and so forth.
Realistically, if you can't pay in the US, any emergency healthcare is free, any maintenance stuff is out of reach.
If you're wealthy, it's not important.
If you're old or poor, you get huge amounts of support.
If you have a white collar job, you get insurance subsidized by your employer, generally.
If you work for government, see above.
If you work in a union, see above.
If you're just well off enough that you get no support, but have a relatively normal income where a hospital bill can ruin you, and you get no subsidized insurance from govt or work, then life is hard.
The ACA makes life easier in many respects, closing some of the worst abuses. However, the ACA is a compromise that makes nobody happy.