There are other uses for the definite article. E.g., "Down the hall and on the left." It's also used in relation to motion. "Go to the left of that ship." Even

There are other uses for the definite article. E.g., "Down the hall and on the left." It's also used in relation to motion. "Go to the left of that ship." Even if you went with it, though, it still has the potential to be confusing. Speaking as somebody who sails occasionally, to me "left" and "port" are just very different concepts. It's sort of like driver's side and passenger's side of the car, but more intense. So I think the desire to use "left" mainly comes from people who don't spend much time on ships, an audience, not particularly important to sailors. Sort of like how non-programmers might struggle with some of our technical terms, but we'd never change.