I don't understand why so many private insurers participated in the exchanges in the first place. It seems pretty obvious that the people who need to purchase from the exchanges are less likely to be healthy than the general population, because they probably haven't had much preventative care in the past, due to their prior lack of insurance, and also because poverty and poor health are highly correlated.

Imagine that you ran a car insurance company, and the government set up an exchange where the least-skilled drivers could purchase insurance. Would you participate?