One of the differences with cargo ships is that cruise ships need a lot of power even when they are at port to keep all the amenities of a large town going. Most cargo ships have tiny crews,and little demand for power when not at sea. They are a significant producer of local pollutants that cause very real health problems for many people.
Some ports do have electrical hookups for the cruise ships to use, but I think they are often more expensive than just burning more bunker fuel, and require to ship to be set up for them.
Cruise ships use a lot of energy, but add up the total energy required to house, move, heat, cool, amuse and feed 4000 tourists and their minders on land and you will also get a large number.
However it seems to be very difficult to change the rules on shipping fuel, but some ports are starting to clamp down on cruise ships that don't hook up to the local grid.
Cruise ships are basically floating Vegases, they are never going to be exactly eco-friendly, but at their available sources of power are limited to those that are badly polluting, even if they use high quality fuel.
The only way to make cruise ships low carbon would be to make them nuclear powered, like an aircraft carrier. You can't really power them with renewable sources like you can with homes on land.
Are they still carbon-intensive? Kinda. Nowhere near as bad as flying, but worse than passenger vehicles and trains. But if we want a fair comparison, shouldn't we also throw in the hotels and restaurants and theme parks that they replace? Because if you get rid of the cruise ships, you haven't really gotten rid of the problem, just moved it around a little bit.
And yes, as I said in my previous comment, cruise ships are like floating Vegases, a large part of their impact is simply the impact of most tourism, but on a boat.
But as I mentioned, a cruise ship can't run on renewables, but a land based resort can. Of course the plane that gets you there is still spewing co2 (I get annoyed by people who fly thousands of miles to go on "eco-friendly" holidays). At the end of the day it's hard to compare these things in general when the specifics of each case matter too.
But even barring the potential for nuclear, renewable power for ships is feasible. Liquid hydrogen has a ton of potential as a fuel source. And it can be reliably produced sustainably with reasonable efficiency. Price is the only factor barring its use currently (the technology already exists, and it is already good enough). With abundant intermittent renewables, excess power will get cheaper, which will bring down the prices for hydrogen. And when cleaner is actually cheaper than dirty, even the ethically-challenged will make the right choice.
If we can generate clean hydrogen I think an awful lot of things that are not easily converted to battery will get a lot cleaner, I think it's being looked at as a replacement for coal in steel production. I think we're still some years away from that unfortunately, last estimate I saw was about a decade, but fingers crossed we get there earlier.
As you say, making doing the right thing cheaper than doing the wrong is the way we solve so many of these problems. Unfortunately we also need to get to the point where it's cheaper to scrap the old kit and replace it, than not, which may take longer.