I worked for one of those cruise companies for a couple of years. First off, my general impression of most cruise passengers is they are either too lazy or too unimaginative to come up with some fun vacation on their own. Some cruisers like the idea of checking their heads out on vacation and not have to think too much about what to do, when, or how. Their itinerary aboard ship or on land is laid out and they must keep to their timetable. Here in Alaska, they often avoid any activity that doesn't put some kind of motorized transport under their butts, boat, train, or bus. I find this ironic beyond belief because they come here to cherish the great natural wilderness in all its untouched glory. What a joke. Of course, the cruise companies control where these mooks visit, where they shop, where they stay, just about all aspects of their visit.
It's amazing how quickly illnesses can sweep through the ship, too. Passengers and crew are hounded to wash their hands and maintain proper hygiene. But when you consider that most of the crew are hired from foreign, third-world countries for wages that would embarrass a robber baron, crews aren't always to be as clean as they could be. Since they work mostly for the tips, they do try to provide decent service to the passengers. That would be tips over and above what the company charges, by-the-way. In cash, if you please.
There's tons more. Would I personally ever go on a cruise? Not even when I'm old and gray...