There are a number of factors at play here. Let us look at some of the most important ones.
First, it is not at all clear to many people that universal health care “has been proven to work well in other countries.” This is a point of a great deal of contention here in the US. There are many people who would argue that the health care systems in other countries lead to things like long delays in being cared for and limitations on what sorts of care people are allowed to get.
Second, and relatedly, Americans are much more certain than people of many other countries that the private market is the best way to provide most goods and services. Americans are very suspicious of most new forms of government intervention in the market. Therefore, they do not tend to believe that government intervention can be helpful.
Third, the government intervention in question is being done by the federal government, not by the states. Americans today are particularly leery of the federal government. They feel that it is especially out of touch with the people and many Americans do not trust the federal government in any way.
Finally, the Americans who are most likely to distrust the federal government are particularly opposed to this particular president. It is not likely that President Obama could do anything that would get much support from conservatives. Even if conservatives might have been able to stomach universal health care of some sort that was proposed by a Republican, they would not accept it coming from President Obama. This can be seen, in part, by the fact that the idea of an individual mandate (requirement that people buy health insurance) was originally proposed decades ago by conservatives but is one of the things that they most hate about Obamacare.
All of these reasons contribute to the strong opposition to Obamacare.