Congress has no Constitutional "power" to implement "universal healthcare," regardless of what you call it. See Article I, Section 8, and the Tenth Amendment.
A change so massive must be authorized by a Constitutional Amendment, and an Amendment requires a super-majority of Americans and their representatives to go along with it.
In the U.S., there are enough Americans who are more than satisfied with the status quo that the necessary super-majority does not exist. Add to the satisfied ones the ones who are horrified at the thought of our healthcare being turned over to the same people who run Amtrak, the Post Office, and the V.A.
But the practical reasons are even more imposing. Unlike other Western democracies, we would be trying to implement socialized medicine into an "industry" that has thrived for generations on a mixed model of a highly-regulated "market" for medical products and services. Changing the game so radically at this stage has never been done before, and would doubtless result in massive fraud, inefficiency, profiteering, and abuse, lifting an industry that now occupies 1/6 of the overall economy to about half. Consider: Congress would never implement any initiative that instantly puts a million health insurance workers on the street; they would be taken care of, one way or another, and we would all have to pay for it.