Why aren't private practice physcians given a max limit they can charge for a single visit?

This is not a question about science, really -- it is more
of a question about politics and rights and economics.  In the United States, at least,
there are a few main reasons why there is no maximum
limit.

First, there is no way of knowing what sorts of
procedures may be necessary in a given visit.  After all, a person might need a lot of
care and there is no real way to know how much the upper limit might
be.

Second, we in the US believe in a free enterprise
system.  If people are willing to pay a lot of money for a doctor visit, why should we
prevent them from doing so?  We do not generally believe in limiting the amount of money
that people can make or spend.

To me, those are the two
main answers.