Something I realized recently is that, to people out east, Lannisport, which is right at the edge of the map, must have something like the same exotic reputation that Asshai has in the west.
Like, for reals. Lannisport must sound like El Dorado to them; a mythical city of gold in the sunset kingdoms at the end of the world, ruled by perfidious, fierce Lion Lords (almost certainly presented as people with the actual heads of lions) who hold dominion over a magical mountain that dispenses endless, glittering wealth. You’d better watch out for their curse, tho. They always pay their debts.
There are probably folk in Yi Ti who dream of going there to get a taste of all that lucre.
It absolutely does have that reputation:
Well, King’s Landing sort of breaks the pattern, but yes, it’s rather odd that two of the biggest cities in Westeros are on the other side of the continent from the main trade routes between Westeros and Essos, and that two of the smallest cities are on the east side of the continent closest to those routes.
But there are decent reasons why White Harbor is small (it’s the youngest city in Westeros, the North is thinly populated), and one could argue that Gulltown’s size might be due to the limited size of the Vale (although I think that’s a bit meh).
The bigger issue to me is why there aren’t bigger cities in the Riverlands, Stormlands, and Dorne.
“The great wealth of the westerlands, of course, stems primarily from their gold and silver mines. The veins of ore run wide and deep, and there are mines, even now, that have been delved for a thousand years and more and are yet to be emptied. Lomas Longstrider reports that, even in far Asshai-by-the-Shadow, there were merchants who asked him if it was true that the “Lion Lord” lived in a palace of solid gold and that crofters collected a wealth of gold simply by plowing their fields. The gold of the west has traveled far, and the maesters know there are no mines in all the world as rich as those of Casterly Rock.
The wealth of the westerlands was matched, in ancient times, with the hunger of the Freehold of Valyria for precious metals, yet there seems no evidence that the dragonlords ever made contact with the lords of the Rock, Casterly or Lannister. Septon Barth speculated on the matter, referring to a Valyrian text that has since been lost, suggesting that the Freehold’s sorcerers foretold that the gold of Casterly Rock would destroy them. Archmaester Perestan has put forward a different, more plausible speculation, suggesting that the Valyrians had in ancient days reached as far as Oldtown but suffered some great reverse or tragedy there that caused them to shun all of Westeros thereafter.”
Casterly Rock is essentially “Gold Mountain,” as Chinese people in the 19th century imagined San Francisco/Northwest America.