A lot of it seems to trace back to a law passed in 1993, which required insurance plans to accept all applicants, regardless of how sick or healthy they were. That law did not, however, require everyone to sign up, as the Affordable Care Act does.
New York has, for 20 years now, been a long-running experiment in what happens to universal coverage without an individual mandate. It’s the type of law the country would have if House Republicans succeeded in delaying the individual mandate, as they will vote to do this afternoon. The result: a small insurance market with very high insurance premiums.