This is actually a remarkably good point. The key concept here is that Bitcoin mining -- even at a "Forex loss" -- will essentially trade electricity for Bitcoins, which can be used to purchase other currencies. Depending on what the miner values their local currency at, this can still make financial sense.

As an example: suppose you are a resident of country X, and you have 1000 XUnits that are valued at 1000 USD, but there are capital flight restrictions such that you can exchange your 1000 XUnits for only 300 USD. And suppose that you need to exchange your XUnits to USD, for whatever reason. You then use your XUnits to buy electricity and mining hardware, and generate Bitcoins, and sell them for 750 USD.

Note that you could try to do the same with e.g. steel, barrels of oil, or widgets, but with hardware you'd be subject to import/export taxes, and the entire operation would have much higher overhead costs (comparatively, setting up a mining farm is pretty cheap).