I have had this song from my earliest days as a folkie, and it has always seemed obvious to me.
A sailors life was strictly male. Cabin boys notwithstanding.

If a seaman fell in love, it would have to be a land-based English girl.

Until the Industrial revolution, most Britons lived outside cities.

Britain was until recently heavily forested. By recently I mean post the development of the English language.

So, a seaman fell in love with a country girl, but she jilted him.

Just my theory.