A question for supporters of the Single Payer or Public Option

We're told constantly that the US spends more on health care than any other nation (save East TImor). In recent years the percentage of coverage by governmental program has risen - from improvements in VA care to the Medicare prescription drug benefit. We also know that, according to the Congressional Budget Office, that the costs of Medicare and Medicaid spending are projected to grow at three times the rate of projected growth in GDP over the next couple of decades - those are two of the three current public options. CBO also estimated that for the past several decades about half the growth in medical costs comes from advances in technology.

Here is the question - if the public option will actually save money, how come it has not demonstrated reductions as the percentage of the health budget has increasingly been applied to the public option of Medicare, Medicaid and the VA?