Until the regime gets the private keys, which isn't unlikely. As soon as cryptocurrencies are widely adopted, regimes will learn about them and not only take the cash but also search for the keys.
When circumventing government, there's also always the question of "how likely is it I will be caught?" and "what happens if I do?". If the penalty is "you get shot in the back of the head" or even just "you spend a year or two in a comfy minimum-security prison" and the probability is "non-zero", most rational people aren't going to assign a high enough value to "not having some money confiscated" to choose circumvention.
Customs can easily catch you smuggling cash, gold and potatoes, but they have no idea you are leaving to cash out your bitcoin in another country.
In each case, the face value is identical but one of the units has an additional possible area of value, extrinsic to the marked face value. You can melt down the silver coin, eat the potato, plant the tulip. This puts a floor on the value of the item - it's worth min(facevalue, extrinsicvalue). Something worth min(facevalue,extrinsicvalue) should be worth more than something worth min(facevalue, 0).
Bitcoin doesn't seem to be something that can be planted, eaten, etc. It doesn't have another area of value, other than being bitcoin.