As the Venezuelan currency is in an accelerating downward spiral the real question is not why such a thing is happening; the real question is why would one sell its US dollars for a currency that is becoming more worthless as days pass. I suppose that we could ask the ancillary question of who but we already know that one: the regime, the military, the corrupt "bolibourgeois", the drug launderers and assorted criminals. People with hard earned dollars do not invest them in Venezuela, at most they use them to pay bills they cannot help but pay.
So why sell dollars/euros for bolivars, even if your return rate is 420+ bolivars for one single USD?
There is nothing for sale in Venezuela. Nothing worth buying. All is imported so you would basically buy something that would be sold to you without guarantee at a comparable world price or at a price that is well overpriced. In bolivars nothing makes sense. But in USD they do not make much sense either. Even cars are now traded in US dollars in the black market and soon in the open one, with quite a mark up.
Buy real estate? Maybe. But what for? You cannot rent, you cannot put it to produce given the crisis. At best it is a very long term investment. The only reason for you to part of dollars this way is to launder them. And all the choice properties have long been sold or are not for sale as people holding them usually have the means to live on something else. Why would they sell they property in bolivares that they would have to go to the black market to trade for dollars right away? They would just make a direct arrangement to have a big chunk of it paid already in dollars.
The only explanation that makes some sort of sense in the current situation is that the regime is selling dollars to pay for its electoral campaign. It has nothing else to offer its voters but cash. By the time they realize that the cash they received is worthless it would be too late. Some inside the regime promote speculation so they can get a maximum of bang for the bug to pay the drag the vote in operation required at the end of the year.
As for the regime, see if they care about the damage that the latest bout of money crash will do tot he economy... the more so that even the NYT is getting on Diosdado Cabello case even if rather meekly.