What would have happened, in that first story, if he had left the ship and swam to a passing boat? Or swam to shore? He was apparently able to leave as later in his imprisonment, the boat drift closer to shore and he swam from there. Why not just leave?

Abandoned crew members often remain on the ship in the hope of eventually getting paid their overdue wages after the legal issues are sorted out. If they leave the vessel then that weakens their negotiating position.