My Opinion to this question:
Why are most of the employees working on cruise ships Asians?
In my opinion, this is due to the willingness to work long hours for a low pay rate (relatively to what Americans or most Europeans would accept) is key. There are also the cultural elements to consider, most Asians have a culture of loyalty towards their employer and are unlikely to go on strike, take excessive sick leave, they are also compliant with tough working policies, for example they are happy to work for long contracts and long hours without complaint.
Interesting to know that, many of these cultures have strong family traditions which means employees could work 1–2 contracts completely away from their families. This adds a stress but, the pay comparing the country of native and, ability to send remittances back to their families makes it worth it. They will work for less money than crew from the US, UK, Europe and Australia, because a wage in US dollars, sterling or euros has better purchasing power in their home countries where the families they support live.
Also in my opinion, the cruise lines do a great job of vetting workers based on “personality.” For instance, the Caribbean staff often works customer-facing food services as they have good English skills and friendly/fun/vibrant personalities. (The room stewards and other “less customer contact” roles are often staffed by Asians that are quiet, respectful, and efficient.)
Most of the cruise line companies also hire from other countries. For many years many ships had Filipino crew members as the majority employees on-board. They have a sea faring heritage and are often serving in deck, and cabin capacities. Most of the officers are from a country of registry; deck: many Filipinos, and a lot of Caribbean crew serving in hotel areas. Entertainment and cruise program are often British, Canadian and US. As the stainless steel Curtain has come down you find eastern European and Central and South American countries represented and even more recently other south and East Asian countries represented. The crews are truly international. There is not an easy job on a ship. The hours are long, variable, the contracts are for at least 6 months if not 1 year. The pay is not great; tips are often the primary compensation. The cruise companies all use agencies to recruit and qualify talent and those agencies have extensive international presence. Crew of course does get food and lodging, but as far as being tourists, they hit the same ports week after week and often spend time in port being on duty. The rules are strict and competition for the jobs is tough.