Simple, there are no dollars to sell to people, where do they supouse to come from? Remember the country has a huge debt to pay.
People use dollars to buy real state, if they can use CEDINs plus if you can regulize this money, it might work out. That explains why the dollar is falling down.
Yet their are dollars to release on to the black market to try and push down the illegal rate, which could be used for legal dollar purchases.
If inflation was low, there would also be more dollars as there wouldnt be an incentive to save in dollars.
If the financial system (and economy, country) could be trusted (in line with lower inflation) there may be more money in savings deposits in banks, less money being shipped out to save in the exterior.
If money laundering wasnt practiced so freely by all the ks and their cronies, there would also be dollars (and euros) in the country.