With the Colorado Health Benefits Exchange in the news, ‘s recent post at Reason is relevant. Excerps.
State legislators who oppose  might nonetheless be tempted to try building and running the exchanges themselves. But there are a number of reasons why governors in that position might want to sit out the implementation process.
For one thing, states won’t have much flexibility to design the exchanges as they see fit … For example, we already know that Utah’s exchange, which does not subject insurers to the mandates required under ObamaCare, will likely not survive. …
…refusing to set up the exchanges … forces the [Obama] administration to take responsibility for whatever inevitably goes wrong during early implementation—and frees governors to criticize the law without also taking part in it. It also ensures that states budgets—which are already in deep trouble—won’t be on the hook if and when the exchanges face cost overruns.