I always thought it was tax reasons people register and flag different nationality on ship, but I guess it is more of a regulation reasons.

https://en.m.wikipedia.org/wiki/Flag...pen%20registry.


Each merchant ship is required by international law to be registered in a registry created by a country,[3] and a ship is subject to the laws of that country, which are used also if the ship is involved in a case under admiralty law. A ship's owners may elect to register a ship in a foreign country which enables it to avoid the regulations of the owners' country which may, for example, have stricter safety standards. They may also select a jurisdiction to reduce operating costs, avoiding higher taxes in the owners' country and bypassing laws that protect the wages and working conditions of mariners.[4] The term "flag of convenience" has been used since the 1950s. A registry which does not have a nationality or residency requirement for ship registration is often described as an open registry. Panama, for example, offers the advantages of easier registration (often online) and the ability to employ cheaper foreign labour. Furthermore, the foreign owners pay no income taxes.