The amount of currency earned from selling crafted items is less than earned from selling the components required to craft the same item. Savvy players don’t bother to craft at lower levels; they only harvest components and sell them (for enough currency to simply buy items and have cash left over).
These players buy up lots of lower level components, turn them into crafted items to grind up their craft skills, and then sell off the crafted goods for almost nothing (the item was just a side effect of the skill-up). Once they get their character to high levels, players begin to desire the end-game benefits of maximized craft skills. They find they have enough wealth to buy up lots of components that seemed very expensive at lower level.