Because trackable doesn't mean "always trackable to a real human identity who's the original source". Bitcoin transactions are trivial for anyone to track, sinc

Because trackable doesn't mean "always trackable to a real human identity who's the original source". Bitcoin transactions are trivial for anyone to track, since everything is recorded on the public blockchain, but you can't necessarily follow the trail to the true culprit even if you're law enforcement. Especially if there are non-cooperative entities in the chain who are completely outside of your jurisdiction. Though, the true answer to your actual question is what the other commenter said: it's mainly due to the Russian government turning a blind eye to it as long as they don't target Russian/ex-USSR citizens. So even if you do know a ransomware operator's full name and home address and everything else you can possibly know about them, you can't do anything about it besides hope they leave the country and try to catch them then.