“Why only on the cruise ships?”
Noro and similar viruses are not “tracked” in the USA. There have been several cases where norovirus hits a school and a large number of people get sick. It will get written up in a local paper if noted at all, and rarely makes national news.
A cruise ship, though, involves contracts and money and many people complaining about their vacation being ruined.
For a ship, they pretty much wipe the whole thing with bleach.
From experience of my 26 previous cruises, I can suggest that you avoid the buffet restaurants on ship, and choose only waiter service sit down restaurants.
The buffets have all adults and children touching the food, and food sits there for hours. Where as in dining room, we always get freshly prepared warm food.
In general, the food staff on ships are much more professional than you will find in family priced American restaurants, in terms of sanitary practices.