There's the cost of setting them up, of course. And if the States don't do it, the Feds will pay for it. But that's the small benefit. Here's the larger one:
...by handing the job of creating the exchanges to the federal government, states can actually protect state-based companies from the ObamaCare mandate that they provide insurance to their employees or pay a penalty
Just like Nancy Pelousy, I didn't read the bill--so I didn't know that was in there. Walker gets it, which is good for Wisconsin.