well you had to have something of value that you had to trade for bitcoin. Also in oppressive regimes the act of attempting to leave the country already makes you a suspect.
They aren't going to immediately execute everyone who is crossing the border. Even in authoritarian regimes, some people may be able to leave, and borders are not completely shutdown.
And in that situation, for those people, it is useful to be able to carry money, in a way where they do not know that you have it.
I mean sure, some people make it out of North Korea. A lot are publicly executed to be made an example of too.
I think you fail to understand the power of a true authoritarian government, particularly if they can monitor and limit your access to the outside world.
* Use a VPN, you're guilty of Treason.
* Use a currency other than the North Korean won, you're guilty of treason.
* Use an electronic device other than state sponsored devices, you're guilty of treason.
All executions will be recorded for posterity and broadcast to the people as a reminder of the power of the state.