the actual rate at my neighborhood cueva yesterday, dec 26, was only 17.75 or so to buy your dollars. Like many internet numbers, these are "theoretical", which is to say, if you are dealing in hundreds of thousands of dollars, you might get this rate. However, on the ground, like most things in Argentina, there are frictional costs which means you and I pay more, and get less.
Which is not to deny that the overall trend is that the dollar will increase in value vs the peso.
I think there are some serious structural reasons that the dollar is so low against the peso- one of which being the hundred billion dollars in debt Macri has issued, denominated in dollars, which brings dollars into the country, making them artificially common, and, therefore, cheap.
Then there is the long held belief that dollars are safer, so many people buy and sell them here.
And, of course, the holiday season always distorts the exchange rate, as people prepare for vacations in countries where the argentine peso is not desired, and exchange rates for the peso are even lower than here.
There are many countries, some much closer physically to the USA, where people conduct all their business in local currency.