Cruise ship manufacturers should do more, but I'd like to see the emissions comparison of those thousands of customers flying to their destinations, then taking small vehicles to reach final destinations.
People fly to cruises so frequently that it is part of a the package system.
Cars aren't going to get you across the atlantic. And planes tend to be more efficient overall than cars in long hauls efficiency wise, both in people carried, and overall efficiency/emissions. Those turbofans are much more efficient at approaching the carnot limit than your small car engine is. Scale matters.