What are the market inefficiencies, other than those perhaps caused by government regulation, to wit, one cannot shop for plans outside one's own state?
If you can shop for plans outside your state, all insurance companies will relocate to the state (South Dakota, Delaware, take your pick) that offers it the least regulation and croniest enforcers, and decline to offer policies adhering to higher standards, and that will be all that's in the market. We can rule that out.
The market is inefficient because:
1. Customers are woefully underinformed about what procedures to get and what they should cost, and it's not realistic for them to become experts
2. People often need health care at times where it's an emergency and they can't comparison shop or do their homework
3. The tax provisions which tie insurance to compensation mean that many companies have oligopsonistic power which hurts everyone outside of them
4. Similarly, with health care as a form of compensation, individuals don't have incentive to know or care what things cost
5. People value life and health in bizarre ways that break market analysis
6. Yes, government regulation
7. Adverse selection
8. Moral hazard