[PeterisP]

Sure, courts cannot freely move Bitcoin from address A to B, but that's not really relevant. The relevant part of ownership in this context is whether moving Bitcoin from address A to B was legal, i.e. did you have the ("ownership") right to act with that Bitcoin? And the answer sometimes may be "no", even if you had the key (which you obviously did, if you made the transaction); the question "whether that transaction was fraudulent, did you commit a crime by making it" depends on who legally owned these Bitcoin, not on who knew the keys.

And in many cases courts can move Bitcoin, and have done so - hardware can be seized, people forced to reveal passwords, and Bitcoin transactions executed. For example, see the multiple auctions of seized Bitcoin by U.S. Marshals Service. They can't be guaranteed to succeed, but that's nothing new (it's not like stolen goods or cash always get recovered), and they certainly can try.

If someone steals something edible and eats it, courts also can't return that thing back to the owner, it doesn't mean that edible things are owned by whoever eats them. In both such cases, the courts can order (and, as much as possible, force) the culprit to compensate the rightful owner - but it matters who the rightful owner (in the opinion of the court) is, so it is meaningful to debate who owned it.