A Pew Research poll conducted in mid-July found that only 27% of adults overall, and 44% of Democrats and Democratic leaners, support a national government-run health-care program with no role for private insurance. WSJ 7-29-19
Virtually all universal systems use private insurance in some way as part of their system. Americans are not and may never be ready to turn over their health care 100% to a federal bureaucracy.
When government is completely in charge with no options it must make decisions that go beyond the payment for care received.
It must manage costs and budgets and to do that it must make decisions about the coverage, how and when people get health care and sometimes who gets it and about the resources available to provide that care.