Ul'dah is centralized because it has access to both other city regions without having to teleport or use an airship. Prior to airships being added, you could not go from La Noscea to the Black Shroud on foot without having to go through Thanalan first.

Jeuno from FFXI was the dead center between Bastok, San d'Oria and Windurst.

Until the world changes, don't expect much to change with the player base. The standards have been set.