Think of it this way. You have say...500 crafter onry players in the game and only 100 battle classes in the game. If those 500 crafters are trying to get those 100 people to buy their stuff, the price is going to come down. Supply vs demand. There is too much supply and not near enough demand. Someone pumping out Crab Bows isn't going to sell them if someone is selling for just 1 gil cheaper.