Interesting, I had to think about this for a moment! It's not entirely intuitive, but I think the answer is "because there's no one else to make liable."
What if the unlocked car was in your driveway, and the person who got in was your seven-year-old daughter? Now who's responsible, and why? The child is a minor, so legally she can't be at fault, but the parents should have taken appropriate precautions, like locking the door.
Likewise, if a bunch of people are killed by a remote driver in North Korea, you can't arrest the hacker. And if there's no one to arrest, our society has no way to discourage the crime. So responsibility moves up the chain.
What if the unlocked car was in your driveway, and the person who got in was your seven-year-old daughter? Now who's responsible, and why? The child is a minor, so legally she can't be at fault, but the parents should have taken appropriate precautions, like locking the door.
Likewise, if a bunch of people are killed by a remote driver in North Korea, you can't arrest the hacker. And if there's no one to arrest, our society has no way to discourage the crime. So responsibility moves up the chain.