The people are in charge of congress, and they consistently show they do not support socialized healthcare systems. It will never be a politically viable path for the u.s, regardless of the economics. Even if it somehow passed, opposition would quickly sabotage and dismantle it.

Obama had a generational mandate and couldn't even pass a public option which, is far more moderate than a single payer approach. Even the abomination of the ACA that actually got signed into law was subsequently gutted to the bone in the following years.

There is room for more tweaking, but the system we're living with now is pretty close to what most voters prefer.