In the last ~6 years I have been on about a dozen cruises. I have been sick on about 30% of those cruises, and have more than several times visited the ship doctor (and have the travel insurance claims to prove it!). I still cruise, but I don’t give them a pass on cleanliness.
A few years ago I was on a cruise from Hong Kong to Sydney, and we had so many cases of Noro on board that Australia almost didn't let us disembark. On day of disembarking, they did a thorough cleaning even before we left... here's a pic of my (wonderful) steward as she prepared to clean (again).
You may not have become ill on cruises, but it is an incontrovertible fact that many, many do.
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