The big one is that many countries do offer foreign currency accounts, but don’t properly hold reserves for them, so the security is there until it isn’t.
These appear to be cases where government regulation was imposed to limit access to foreign currency. Not, as you seemed to be insinuating ("but don’t properly hold reserves for them"), any problem with banks carrying insufficient reserves.
So, there was neither a technological problem moving fiat in our out of the country that would be amenable to a technological fix, nor unintended weaknesses in the regulatory regime covering local banks. Rather, it was deliberate government policy.
> These appear to be cases where government regulation was imposed to limit access to foreign currency.
It’s not « access to foreign currency », it’s « access to your own deposits ».
Cuz the banks and/or the central banks spent/seized the foreign currency before you, the depositor, could spend them. So much for trying to protect your assets by holding them in foreign currency.
