It's a cheap way for the regime to reward supporters without actually having to come up with any real dough. Anyone supporting the regime has safe, easy means of exploiting currency arbitrage whereas ordinary people are policed heavily. Show up at the airport with a suitcase full of US dollars and depending on your political status the customs agent will either close it back up and send you on your way, or perp-walk you straight to jail after confiscating your haul. (guess where it's going?)
It's also why one of the first demands the IMF makes on broke states before they'll lend them money is to let the official currency rate float.