It's one thing to sail a carrier group around the world.

It's very different to have a reactor sitting on a cargo ship, hundreds of miles from anyone, alone in the middle of the ocean.

The three named ships all proved nonviable. Savannah, a liner-cargo combination suited neither role well, the Otto Hahn was simply uneconomical though was later converted to diesel, and the Mutsu had significant technical issues as well as political resistance. Whether or not low fossil fuel costs of the period (1962 - 1990, roughly) had a major impact isn't clear. Nuclear power requires very highly trained crew, however.

Another factor working against larger-scale marine propulsion deployment is the number of shipwrecks. Roughly 200 major vessels are lost every decade or so, which if a significant fraction were nuclear powered would be a large number of reactor cores littering highly trafficked sea lanes, many of which are shared with fishing and other uses. All told, there've been on the order of 400 or so marine propulsion nuclear powerplants deployed in total (most on submarines), whereas the commercial shipping fleet is on the order of 60-80k vessels.