The very basic answer is those taken on as "staff" on ship will not be there for longer than one tour if the lifestyle on ship and the pay does not suit them. For those that know how to "play the game" and they have accepted the lifestyle that come with it. They know how you can money from folks on this wandering, full of misfits and aholes floating hotel....So they deal with it and work it in the same way that other folks working on land do the same thing everyday in their normal "job",,,,,dealing with people and all that goes with it.
Okay you work on a ship, some will be crap at it and go, others will play the game, make it work and gain those extra bucks for the time that they have the stiffs to make it financially work for them. So it does not matter where you come from either the US, UK or Somalia, are you as a person prepared to do what it takes for 5,7,10 or 14 nights to get out the people presented your expected income?? Sadly not a lot can,,,play the game that will make them money.
Folks don’t actually realise that if you are prepared to give up your personal life and move away from being with your family everday, that there is a lot of money to be made on ship if you approach it in the right way.