I am a knitting history lover (and Irish to boot), and was disappointed to see that the leading scholars agree that the identification at sea theory was not actually true. It may have been a de facto consequence, but it wasn’t intended.
However, the cables were more than just attractive stitch patterns. They were used to add warmth to the sweater, to make the sweater thicker. There is some evidence that different stitches have different meanings as well. For example, the Trinity stitch was used to provide the protection of the Holy Trinity over the wearer of the sweater.
Also keep in mind that it rains a lot in Ireland, and being at sea would require a lot of exposure to water. Wool is wonderful in that it can absorb 30% of its weight before it starts feeling wet, it’s naturally antimicrobial, and it’s one of the few fibers that still insulates when it’s wet. So you can wear a wet wool sweater, and it will still keep you warm. So a thick wool sweater would have been not just attractive, but extremely practical as well.
Sorry for the novel!