With the possibility of getting down voted into oblivion. The BTC lost/stolen are all available within blockchain/public ledger. Depending on who stole them, it would probably be distributed within multiple very smaller transaction. It my be traceable, but likely unrecoverable, because this is a feature of Bitcoin. In other words authorities and forensic enthusiasts can find the BTC but they are most likely lost at t…
The thieves will move funds around at little cost in order to try to gain the value from the Bitcoin they stole.
The problem with Bitcoin is that because there's no fee associated with them, there's no money or resources being made available or directed towards policing and following of these thieves.
Edit: And it's not particularly fair to use the rest of society's resources to do this policing, when they're not contributing to the system - they're avoiding contributing, to a partially corrupt and currently inefficient system, yes - but it'd be better to fix these inefficiencies and deal with the corruption.