If there aren't staff on the cruise ship to remind you to brush your teeth, to ensure you take the correct pills at the correct time, and to help you get to the toilet several times per day, then I don't think they're comparable at all, before actual medical care as in treatment or rehabilitation of any kind enters the picture.
Ability to tolerate and care for residents in severe mental and mobility decline are kind of the differentiator between a nursing home and other kinds of lodging.
