A crossing and a cruise both involve a large passenger ship and several days at sea. Almost everything else about them, including the shape of the hull, is different.
A crossing has a schedule to keep
A crossing exists to move people between two fixed points in a set number of days, in whatever weather the ocean produces during that window.
A cruise is a round trip that returns where it started, and its route can be adjusted around weather because no one is depending on arriving somewhere specific.
That difference drives the engineering. A ship that must hold a schedule needs the speed and the sea keeping to maintain it in poor conditions.
Hull form follows the requirement
A vessel designed for open ocean work tends to have a longer, finer hull with more freeboard forward and a deeper draft than a cruise ship of similar capacity.
Cruise ships are optimized for calm water, port access and interior volume, which favors a fuller hull with a broad beam and high superstructure.
The trade shows up in fuel. A fine hull driven fast burns far more than a full hull moving slowly between nearby ports.
Speed is a design decision, not a setting
Sustained speed on a crossing is set by installed power and hull resistance, and it is the number the whole schedule is built on.
Cruise itineraries are written so the ship rarely needs its full speed, which lets operators run economically for most of a voyage.
This is why a crossing at a comparable fare is a different cost structure entirely, with fuel a much larger share of the total.
Weather is absorbed rather than avoided
On a crossing the ship alters course to reduce motion where it can, but the passage must still be completed, so passengers experience whatever the ocean delivers.
Open decks are closed, outside doors are secured and public rooms are prepared, which is routine rather than exceptional on a North Atlantic run.
Cabin choice matters more on a crossing than on any cruise, since several consecutive days of motion amplify the difference between positions in the ship.
What the format offers a traveler
A crossing gives a long block of uninterrupted sea time with no port days, which suits people who want the passage itself rather than destinations.
It also removes the flight in one direction, which is why some travelers use it as transport rather than as vacation.
The constraint is the same one that has always applied. The schedule runs when the operator sails it, and the return is by air unless the timing happens to match a crossing the other way.