When people talk about the Bard’s poetic sense, they’re usually talking about the meter, the rhyme schemes or the images. I see it here as well. Roll this line around in your mouth and you’ll see that it just feels good. There is rhythm and a satisfying symmetry to “Sailors, my lord, they say.”
And yes part of that satisfaction is how it fits (and doesn’t fit) into the Iambic Pentameter but part of it is the balance of Ss and Ls. The assonance, the alliteration in a 6 syllable sentence. A word like lord sits comfortably near a sentence with sailors and saying. So pleasurable. Sssssso pllllllllleasurable. Letters. Words. Even in the mouth of a lowly messenger.