Who says those aren't Americans on those cruises?
Where were the cruises based? Since there are restrictions on travel for Americans to quite a few countries, it might limit their number. OTOH, those restrictions are probably porous.
My brother lives in a semi-rural area north of Montreal where many of the country properties are owned by Americans. He says the number of US license plates around town is no different than it ever was. I believe that property owners from the US can go to their properties but are supposed to self-isolate for 2 weeks when they get there. Maybe some are doing that and many some aren't, hard to police everyone. High compliance helps in the fight against viral transmission.
I suppose it's no different than with crime, in the sense that authorities (police, etc.) can only really keep a lid on crime if the rate of criminal activity is low. If a large percentage of a population is committing a crime, attempts to control it will be futile, as the war on drugs has shown over the decades. So we try to hammer home the way to prevent transmission, keeping up the messaging, but in the end if a large percentage of a population decide to not listen, people will suffer. If you could guarantee that only those who did not follow guidelines would suffer, you could at least find some comfort in that the "correct" people paid the price, but this is not the case with this virus as innocent bystanders will suffer, as is usually the case. So we rely on cooperation, not an easy thing to obtain in general over long periods of time.
