It's because of the fundamental physics involved. When you give somebody is a paperback book it is fundamentally a "move" operation. When you give somebody a s

It's because of the fundamental physics involved. When you give somebody is a paperback book it is fundamentally a "move" operation. When you give somebody a software program it is fundamentally a "copy" operation so the original owner still has it. The only way to simulate a move operation is to follow the copy operation very shortly with a delete operation on the original media. Of course if you are copying data from a device that you own then the manufacturer or media owner has no way of knowing if that delete operation really happened. So they try and work around this with increasingly sophisticated methods to force a delete operation. However these are usually not effective against a determined attacker, so the easiest thing to do is simply to disallow the move operation altogether.