I think the change from steam to diesel-electric has a lot to do with the visual design of the ships. There is no need to have multiple huge exhaust vents directly above the boiler banks, so they can build the superstructure higher and create more cabin space (thus more revenue). Ships now are basically floating resorts - you visit for a week or 2 but almost every cruise ticket sold ends at the same dock it left from. Ships used to be the primary the mode of international travel, now they are just giant party barges.
Even on the new ships, most of the really heavy stuff is down in the botttom, which gives a safety margin for roll over. Older ships didn't have stabilization which limited how high the superstructure could be, not just from a safety standpoint but comfort as well. When the Triumph lost power out in the gulf a few years ago, it was still safe from a rollover perspective but people reported that the rolling motion on the upper decks was far worse than down closer to the water line.
I took a cruise in the early 1990s on a non stabilized ship. It had originally been built for transatlantic service (I think late 1950s-early 1960s vintage) and was an actual steam driven vessel. It was quite comfortable even 5-6 levels above the waterline but I couldn't imagine what it would have been like 16-20 floors higher. It had been reworked multiple times as it changed owners, but it still had a lot of that classic steam liner look to it. I was in a lesser-priced cabin only 1 level above the waterline and the motion there was very faint. That ship also had a 30 foot draft, amost like a 700 foot long deep-V hull.
A few years ago I went on a cruise (on the then refurbished Triumph about a year after the infamous "poop cruise") - the stabilizers worked remarkabiy well - you would feel the ship start to roll and then it would just stop, then a few seconds later you would just start to notice it going the other way and just stop. It was solid enough that the onboard minigolf at the top deck was perfectly playable. But the modern ships are basically giant Jon boats - very flat hull with much less draft. Without stabilizers they bounce around a lot.
One of the reasons the SS United States has such a long lean and low appearance is because it was also meant to be freaking fast - fast enough to keep up with a cold-war era carrier battle group as a troop transport should the need arise. And probably fast enough to have at least a reasonable chance to get away from hostile nuclear subs of the era as well.