>The bitcoin part makes it non tangible and could be done from anywhere in the world.
It streamslines it, yes, but it doesn't make it "almost impossible" to pull off like gp claims. Russia is listed as a "high risk" area in the wikipedia article for ransoms, so if they can pull off a ransom exchange (with human hostages) there, I can totally imagine russian hackers being able to pull off a ransom exchange with cryptographic keys. If anything, it's probably easier to pull off than a regular ransom because you don't have to contend with a human hostage.
Also, a quick skim of wikipedia[1] suggests that buying/selling of stolen credit card info predates the creation of cryptocurrency. If cybercriminals were able to find ways of transferring money back then, I'm sure ransomware authors can use the same methods to transfer money today.
[1] https://en.wikipedia.org/wiki/Credit_card_fraud -> https://en.wikipedia.org/wiki/Albert_Gonzalez -> https://en.wikipedia.org/wiki/ShadowCrew