I'm not sure even the cruise lines have accurate data as so many people are choosing not to report symptoms anymore because they don't want to have to quarantine. And people who don't test positive until they get home don't report back to the cruise line. With less testing happening (beyond the pre-cruise test), the cruise lines aren't going to have much data.
I just assume that when case numbers are high on land, they are likely high on a cruise ship. Anyone who isn't comfortable hanging out at a restaurant/bar/concert at home, probably shouldn't go on a cruise.