That’s because they were.

All of the ships mentioned had been built years earlier and (for the most part) for the sole purpose of moving people from one continent to another. Something happened in 1924, though, that threatened the economic well-being of the steamship companies: the end of mass emigration from Europe to the United States. Companies suddenly found they owned too many ships for the trade, at least on American routes, and had to find something to do with the surplus tonnage. What’s more, many of the facilities originally installed on these ships (such as opulent dining rooms, covered promenades, and the like) were out of style by the 1920s. So the steamship companies invented the idea of the cruise. They redecorated and reassigned rooms and deck space, turning what was an overdecorated (for the time) first class entrance into a pool or an out-of-date gym into a boxing ring. They then promoted the idea of actually taking vacations on a ship, rather than having the ship be merely the way one got to the vacation site. In this way they were able to delay the implosion of the industry until the Depression killed off international travel.

There are a lot of refurbished anachronisms in the vacation industry. Those lovely Swiss and upstate New York mountain resorts were once tuberculosis sanatoriums.