I don't think half the replies here realise just how remote and dangerous the Sea of Thieves archipelago is and how difficult it would be to construct a large settlement there.
Outposts are about as populated as it would get... a village, which is smaller than a town and has 500-2500 inhabitants would even be unlikely, never mind a city.
This is somewhere the GMU have failed to infiltrate in any great numbers - their fleets held back by the Devil's Shroud. The only sign of them is their supposed connection to the Emporium.
Point being that journeying to the Sea of Thieves is not easy and it's not somewhere people go to live in an organised society that a city would require... it's a place pirates and adventurers go to find freedom and riches, and answer to no-one.