Muad'zin
Fractal Fanatic
Not at all, but there's an element of time here - a lot of great art will have been stolen at some time. Stuff can be stolen and recovered, or stolen and then the insurance company pays out and after 10,20,50 years likely writes it off as unrecovered.
Of course thieves should be chased, hounded etc. but there are a lot of nuances once you start getting a long way away from the event
Time is the great equalizer, but as long as the victim is still alive, the criminal should never be off the hook. And if you knowingly purchase a famous guitar that was stolen you become part of the crime and should be treated as such. And I reckon these guys know it, otherwise they would not keep their stolen loot hidden in their private collections.