The lowest income people in the US also qualify for free healthcare through Medicaid. It covers ~20% of the US population (that number also includes those with disabilities).
Medicaid simply isn't the healthcare panacea for the poor that some make it out to be when they say, "But the poor already have coverage!". And it ignores the fact that there's millions of people just above the income cutoffs whose state of poorness is pretty indistinguishable from those that get coverage, but they're still completely on their own.
First: 400% of the poverty line is not very high, so premiums for people just over that line can still be very unaffordable.
Second and more importantly, ACA coverage is generally not very good, especially at the low silver tier covered in that %10 income cap. Pointing at the ACA ignores the fact than plenty of people with coverage still are faced with insurmountable debt, sometimes loss of home, and often bankruptcy. As long as hundreds of thousands of people each year have bankruptcies tied to medical issues, there's nothing about the US system you can point to, be it Medicaid, Medicare, ACA subsidies or anything else, that can surmount the argument that the US system fails people in this respect when compared to other countries with universal coverage.
I'm not saying those countries are always better in every respect, but one thing they have is that they don't cause their citizens to lose their entire way of life, their home, and ability to live above poverty levels when faced with treatable medical issues.
The tax burden is higher because education, public transport, agriculture and social (mostly retirement) are paid in tax rather than mostly privately.
US has the private system for retirement plans and it sometimes fails utterly. The nationalized one does not, though it may not be as big of a payout. And education saddles people with debt, as well as causes cost (admin) inflation.