When you port somewhere, you can rent a vehicle or take a taxi to places not in the port town. If you want to travel to various tropical islands, you can fly or float, it's not like there are a bunch of transportation options that can take you everywhere.

I'm not saying that rail is a worse option, I'm saying that cruises are fun, and that's why people go on them, which was the initial question I responded to.

Clearly you've never experienced what a cruise is like. You're coming to these conclusions that just aren't based on reality. A cruise ship is a small town full of entertainment. If there were no entertainment, yea, floating in the ocean would get boring after a few hours, unless you're into that kind of thing. They are mobile resorts, and when you wake up, you're in a new location. They aren't over crowded, except when everyone is boarding and leaving, but that's true with literally every form of mass transportation.

Some people take cruises and never leave the boat. They like to relax by the pool, enjoy the spa, partake in on board activities, gamble in the casino, eat all of the included free food or drinks, or whatever.

I'm not defending the environment part, or the legally sketchy stuff, but they're entertaining.