I was asking rhetorically since the graph makes it pretty obvious, but actually re-reading this article it's a bit more complex than I recalled. There was basically some legislation in the mid 1970s that made them possible, the model grew through the 80s, but by the late 80s low-rent HMOs had taken over, and a crippling combo of regulation (to create new barriers to entry) and deregulation (for the existing guys) basically cemented the for-profit HMO/PPO providers that we all know and love (haha) by the 1990s. Had we held out for another decade we probably would have seen socialized medicine by the Clinton-era, but instead we got this graph, where we pay more and get less than everyone else, and half the country thinks it's a great idea.