[chiph]

There's a couple of reasons why the crew and officers don't just leave. One is that their employment record will show that they left their ship while their contract was still in force, which given that jobs in the industry are highly desirable will make them unemployable.

And the other is that the port authority wants the ship gone, and not vandalized or becoming a hazard to navigation. So they will require someone to stay on board to maintain it and keep it secure. Which can include getting Immigration to forbid the crew entrance to the country. While they are in port, it's much like being in the secure area of an airport - they're in a gray area and aren't actually in any country. So when that happens, it is illegal for them to leave it.