Because a state’s employers and residents become subject to the law’s mandates and penalties only when subsidies become available within its borders. So long as only state exchanges are authorized to hand out subsidies, states can shield its people simply by refusing to implement an exchange. But if the feds can extend subsidies, this shield disappears. In essence, the state becomes subject to the diktats of a law it has officially rejected.

Forcing states like this would never have passed muster in Congress given the fragile support for the law at the time. So the administration’s choice was to pass the law without such subsidies or kill it by including them. Letting the IRS extend subsidies would mean letting unelected bureaucrats “commandeer” states, something Congress was unwilling to do.

Some courts might be willing to allow this, but it’s unlikely all will. More likely, they’ll split and the matter will reach the Supreme Court. This will take months, possibly years, to play out.