Obesity plays a big role in Covid-19 deaths. 33% of Americans are obese, and 65% are overweight. There's a possibility that more obese people take cruises--it fits their lifestyles (unlimited food availability, and they don't have to move much). So the DP data may be tempered by more obesity even though it has less extreme elderly.

Also many of the crew got infected. So the amount of viral exposure may play a big part. People who had to come in contact with dozens of infected individuals every day may be the most vulnerable. This doesn't bode well for retail grocery workers.