The reason that we are planning a yearly cruise-vacation, for the next few years, is that we are getting up there in age and we cannot do that much anymore.
It would be nice to go to one city for a week or so like Boston, Paris, Barcelona, etc, on our own, but that would involve a lot of walking. In addition, we can only do a 4-5 hours tour/per day. Which means going back to the hotel for the rest of the day. On a cruise there is a lot of activities, including shows, after we get back to the ship. Not to mention, that all the food is included - no need to search for restaurants.
We believe that cruises are the best vacations for senior citizens. In my youth, many but many years ago, I would not had dreamed of going on cruises.