The Price of Progress
Pirates are a natural occurrence in any seafaring nation. The pirates found in Earthsea tend to be extortionists more than plunderer, similar to what one my think of as a mob.
Most often they tend to sell protection to local merchants: protection is that is only needed if you don’t pay for it. Occasionally they will stop non business vessels and ask for a “toll”. The trouble they cause tends to be proportional to the trouble they get (ie., do what your told and there will be no trouble).
The largest and most famous group of pirates are those of the Closed Sea. This offers them close access to the inmost sea, and therefore most of the industrial trade routes (Wathort, Havnor, Ensmer. Paln and Osskil being too out of the way), while still giving them undeveloped lands to hide in. O-port tends to welcome the extra cash flow from the group, and even tends to be a vacation spot for those without children.