Why have 165 people gone missing from cruise ships in recent years?

Why have 165 people gone missing from cruise ships in recent years? | Mail Online: "On the evening of April 6 this year, John Halford packed his suitcase and left it outside the door of his cabin on the cruise liner Thomson Spirit. It was the last day of a week-long Egyptian cruise and the ship was due to dock at Sharm-el-Sheikh the following morning. "