YES ... there is COVID on the cruise ships and it doesn't matter if it is 30% or .03% if you run into the 1 person that has it you can catch it. It is very contagious. But there is also COVID in your neighborhood. My husband or I got COVID from a visit to the grocery store, hair dresser, LabCorp, pharmacy or department store. Not sure where but probably just one of us got it and gave to the other. We only had slight cough and tested because we were going on a cruise. Otherwise we would not have tested. Does everyone else test if they cough?
And ... the people who test after the cruise probably got it on the cruise but could have gotten it going to/from the cruise (flying, stopping for gas or lunch, etc.).
I agree with others ... if want to be sure not to get COVID on a cruise then you should NOT cruise now.