Cruise ships are actually well set up for quarantining the infected, once identified, and limiting the scope of infections. Outside one’s own room, things are pretty open, rather than enclosed, and cruise ship lines have been adding UV virus-sterilizing apparatus to their HVAC systems, as have the airlines. UV additions to home HVAC systems will likely become a standard in time.
The Diamond Princess didn’t have those, and it didn’t lead to all the passengers (mostly elderly) on it dying, did it?
And that was the original variant, not the (less lethal) Delta.