I used to enjoy mooning them in Cozumel. As we passed them on the way to the southern dive sites, there were always a few people with such boring lives that they would stay on board in port and watch life pass them by from the stern. Then I decided I was being cruel to sad people.
You are being pretty judgmental. Sad people? Some cruisers stay on board at some ports because they have been to that particular port enough times to have done all of the excursions that are of interest to them. If they don't dive or snorkel, the tourist attractions look the same as the last time visited. Some stay so their kids can have endless turns on the numerous "active" activities available on the larger ships. Others stay on board because their purpose of cruising is to detox from very stressful work schedules or family issues. There is nothing sad about having the freedom to do exactly what you want to do with your day, when you want to do it, and for how long. To paraphrase a comment I often hear from people (especially wives and moms) returning from a cruise "I thought I died and gone to heaven: Sleeping late; having very nice meals that I don't have to cook or clean up afterwards; having the luxury of all family members eating what they want without me being a short order cook, enjoying the pool, hot tub and spa; seeing local sites (including diving) if I choose; taking in a nice show every night; kids' clubs that provide fun and safe entertainment for my children; and time for myself. I just wish I could afford to do this more often." I have never heard anyone say "Gee, I can't wait to go back to work or housework on Monday." Of course cruising is not for everyone, but I would never describe anyone I have ever met on a cruise as "sad people."