In the waning days of the Great Kingdom, folk who were faced with debts they could not pay or disagreements with the legal authorities that might see them imprisoned or facing the hangman often found it convenient to flee narrow area of flatwood, sandhill, and wetland along the Northwest edge of Wooly Bay. There, they would be, if not welcomed, at least accepted into the independent community that had grown up among the several, squabbling towns. The region had an infamous reputation and was known as the Wild Coast.
Primarily, the Wild Coast served as a safe haven for brigands and outlaws from the woodlands west and smugglers and pirates from Wooly Bay to the east. Trade went on between the groups without fear of Dyvers' or Greyhawk's tax agents. The towns grew up to crater to the needs of these clientele but also drew others in search of freedom: escaped serfs and slaves, political dissidents, fringe religionists, and more than a few nonhumans.
The freedom of the Wild Coast was just as often manifest as lawlessness. Existence was precarious when local powers shift quickly and much of the population is transitory. Humanoids raided up from Pomarj and monsters driven out of other areas sometimes found this sparsely populated region ideal.
It seems like Gygax wanted the Wild Coast to evoke a bit of the American "Wild West." I drew inspiration from a number of places: the Romagna during the late Middle Ages/early modern period, Barataria Bay in the early 19th Century. Mostly, it's just a fantasy region though.