Well:

• It's much more feasible to develop nuclear-powered or even partially renewable cruisers/liners than it is to develop equivalent aircraft. Without having to expend huge amounts of energy in staying aloft, ships really just need enough energy to push their mass through the water and power the ship's systems.
• Ships can be made into highly efficient closed or nearly-closed loops, it's really just industry laziness that stops this from happening. Outside of safety regulations, shipping is not regulated to anywhere near the extent of aviation.
• Because aircraft emit high into the atmosphere, the effect of their emissions is even worse than it is at sea level. Ships don't have this problem.
• Cruisers visiting small ports can bring significant economic benefits to coastal communities, it's just that right now those benefits are linked to disgusting corporate extortion. Regulation can solve this.
• Ships don't have much associated noise pollution. Airports and even trains are loud and often a nuisance, but even dozens of ships entering or leaving the harbour on a daily basis won't be a loud affair.
• When a ship capsizes, there's usually much more chance of people getting off alive than there is escaping from an aircraft. Aside from accidents at airports, when was the last time you heard of a scheduled airline accident that didn't kill everyone on board?
• Liners can make a Transatlantic crossing in around three or four days with current technology, and if airliners hadn't killed them off we might have seen nuclear-powered liners make it more like two. That's fast enough to be a viable alternative to flying for leisure, if aviation was properly taxed.

There are lot of conditionals and uncertainties when it comes to making marine travel great again, but eventually we might have no choice but to at least try. The technological gains left for modern aircraft designs to make are vanishingly small when it comes to fuel efficiency, all while the aviation industry continues to grow unabated. Next-generation liners and cruisers might be a way to stymie that growth, at least a little bit.