Indeed, it is quite striking. At 218 confirmed cases, the plague ship is home to far more infections than even the second highest country - Singapore at 67 confirmed cases. I suspect there are at least a few factors at play:
1. Cruise ships are floating petri dishes - note how norovirus spreads like gangbusters on a cruise. Lots of people in very close proximity, often lots of interactions with greater numbers of people (i.e., on a cruise, you meet lots of new people, whereas at a shopping mall there are lots of people, but very little interaction), lots of recirculated air (like a flight, but instead of hours, a cruise can last for weeks), lots of meals being prepared by staff who are also subject to the same infection but even worse, because they spend much longer on that floating petri dish than the passengers - and compare the food handling by staff on a 2 week cruise vs 4hr flight, both in number of meals as well as opportunities to contaminate the food (mostly getting pre-prepared, wrapped/cover food/drink on flights).
2. They are testing everyone on the plague ship (or I believe more accurately, everyone who has had contact with someone who has been infected, which probably means most on board will get tested); on land, we are only testing those who show up at hospitals (in China), or those who present symptoms AND had recent contact with someone from Hubei (most of rest of world). So it could be that, on land, many infections go undetected (seems likely) because people don't show up at hospital or their doctor, because their symptoms are very mild/fleeting or it amounts to a flu that they ride out at home. This may actually be a good thing - i.e., maybe for most, this is essentially another flu-like virus and once it sweeps the world, we will have herd immunity the way we do influenza.
3. Cruise is in East Asia, so it's likely that the demographics of the passengers reflects this. Thus far, East Asians seem far more susceptible to severe illness from Kung Flu than others. Seems most others are able to shake it off like a cold or flu. Not clear why, but some suggestion that it's not ethnicity that is playing a role, but cigarette smoking - and Chinese love their cigarettes, especially men, which might explain why in China, there are significantly more male cases than female cases.
What is really crazy is that apparently a Japanese doctor boarded that ship to take a look around and he is now infected. WTFBBQ! I would assume that by the time he boarded, he knew how transmissible this virus is, and would have taken all precautions, and he wouldn't have been there for very long (hours at most), and yet he still got infected. Of course it's possible he was infected at the hospital (1700+ infected medical personnel in China - that CCP has admitted to) and only developed symptoms (and thus got tested) after visiting the plague ship.