To play the devils advocate, linking health care to your job means that productive citizens are being taken care of. This fosters a "survival of the fittest" situation.
That isn't really how it plays out, but I think that's the allure to many of us Americans. I've spoken with others who who believe that you must work to earn certain things, such as health care. It is often toted that people who are obese, smoke, do drugs, and participate in other health risks are more likely to be on government aid than those who "earn" it. They use this fear of being taken advantage of to fuel a desire a knee-jerk reaction to health care.
Yet there are valid concerns. Especially with the migration of such an entrenched system.
If the US government is going to take on Health Care that money needs to come from funds already in the budget. The US government is poised on the edge of failure, the only thing keeping us going is a mass faith in the ability of the government to pay back it's loans, and thus receive more.
Also this points to a bigger break in the system. US Agencies (I can't speak to foreign agencies) incentivise the spending of your whole budget. If you don't spend it all then obviously you don't need it all. This creates a mad spending rush at the end of the fiscal year and an atmosphere where you have not only the right but the obligation to spend your budget.
I think a lot of people are intimidated by the concept of introducing another burden to the US budget when we are already incentivising the wrong thing.
I think if we could cut back the budget in other areas, this would make it possible to introduce a true health program.
I'm only touching on a few reasons why this isn't being done immediately. I do think that our defense budget is outlandish and could be put directly towards health care, but that is a huge transition in the work force. That is soldiers to medicare specialists. That sort of transition will take time.