You don't need to be particularly fit or healthy to go on a cruise. Yes, sure, you can't be on life support, but generally 'healthy enough' to travel on a cruise is exactly what I'd expect from any random sample of the overall population.

The problem is the disease is mostly killing off the least heathy. Exclude only 5% of the population and deaths might easily drop by 1+%. Further the Dimond Princess was evacuated specifically because they could not contain the spread. Suggesting their rate of infection is indicative of anything would mean we had somewhere to be evacuated to.

You may not understand what "random sample of the overall population" means if you would expect every single person in the sample to be healthy enough to travel on a cruise. Almost 1% of the population in the US has Alzheimer disease or other dementias, for example.

I noted exactly that in my comment. Yes, not all the population can go on a cruise. No, it's not like it's only the healthiest 20% of the population that can. If I randomly sampled the population I'd expect the majority to be capable of a cruise. What do you think cruises are like?

It's been hitting those in assisted living facilities rather hard, and those people would likely not be able to take a cruise.

If you agree that they are not a random sample of the population - they are healthy enough to be fit for travel (like the majority of the population) you are not trying to contradict ant6n's comment as I thought. I misunderstood, my apologies.

and it's not a small travel (e.g. the British tourists that went on board the Diamond Princess).

If you are not in good health at the beginning, you don't adventure yourself 10 hours+ from your home. So this group is likely in better shape than average population.

Isn't the average age on a cruise ship far older than in the general population? I would've thought the people on board would on average be far more vulnerable.

It’s a narrow band excluding the young and oldest so, the average is older but the maximum is younger. With a very sharp decline in their 80’s, which is when things really get bad.

Considering how quickly the numbers get worse with age and ill heath many countries are at higher risk.