Wait, what? The Jones act is for protection of domestic-flag carriers and prevents cabotage. How does such an act make it advantageous to be foreign-flagged?
No US minimum wage or US monitored working conditions. No FICA taxes, social security, medicare taxes.
All cruise ship companies fly flags of Panama, Liberia or some other foreign country.
The Jones Act states that if you are a US flagged vessel, you must comply with US laws for the workers on the ship. That means they need to have working conditions, safety standards, pay standards, etc. That also means they can be sued in a US court just like your/my employer can be for all sorts of things like sexual discrimination. Being a foreign flag of convenience vessel makes it A LOT cheaper to operate. That is why these cruises are so cheap in comparison to staying in a US resort on US soil.