That's why U.S. health care costs have tripled the rate of inflation for three decades. Insurers have no incentive to moderate health care costs, only how much they profit -- so naturally they insure the healthiest, and make it hard to get help with pre-existing and/or expensive conditions.
Sometimes they even countermand medical decisions. Bureaucrats worrying about their bottom line can over-rule a licensed doctor's prescriptions and treatment orders to protect the corporate profits.
There's no real choice when an individual enters the health insurance market. They bundle in with the group at work, which has a very narrow range of choices - and every insurance company makes about the same markup on the same basic services, so the costs (concealed in overly complex plans) aren't all that different.
The government's role in fixing the system for our mutual benefit is to model efficiency - at least until big insurers learn to deliver their services efficiently - to compete.