Maybe it's worth reminding that a ship in the middle of the ocean is often much farther away from any other human beings than the astronauts on the ISS, and tha

Maybe it's worth reminding that a ship in the middle of the ocean is often much farther away from any other human beings than the astronauts on the ISS, and that sending a rescue mission from ashore to fix a leaking pipe would take a long time and a great amount of fuel. Therefore it makes sense to have at least a few people onboard for basic servicing. Also maybe worth remembering that once close to the departing or destination harbour, any large cargo ship met with the harbour pilot team who goes onboard and take responsibility for manoeuvering the ship, so no ship would be unmanned the full course of its journey anyway ; only the easier, longer part.