I got here:
Congress created a system for providing tax subsidies and penalties in order to give incentives for people to buy health insurance or for employers to provide it. States were supposed to create new agencies that would offer online insurance-shopping options, and states would tie into a federal tax system to dole out the subsidies and assess the penalties.
But the ACA made clear, Adler says, that the subsidies were to be used in these new state marketplaces, or "exchanges." There is no record, he says, that shows Congress directed the subsidies to what has since evolved: a large, federally run, health-policy shopping exchange. When the subsidies are mentioned in the law, Adler says, it is always and only in the context of state exchanges.
Congress did provide for the creation of a federal exchange, but as a backup, Adler says.
And stopped because is that saying:
Congress talked a lot about doing "A" ... except when it talked about doing "B" because you won't/can't do "A"