I remember a time where i could easily live in Gridania. The carpenters guild was really busy.
As the world population decreased, people started to drift more to permanently staying in Uldah.
As time went on, i was spending more and more time in Uldah because it was the only viable city to buy/sell/trade.
There seems to be a critical mass where if the population drops too low it becomes quite difficult to play the game outside of Uldah.

Ishgard is the key to everything.