No one sees the item market as an obligation. But many people who play for a long time make use of this market within the game, and the possibility of modifying items in an unlimited in the tempering, way would end this market.
Not only that, the items would become usable by all characters on your account. That is, once dropped, the item would never need to be dropped again, as you would change and modify it as you wish, so that it meets the needs of the vocation (druid, barb, sorc, …).
It would be a final item, and you could use it infinitely. You would never break or sell that item again, and there was no need to farm new items anymore.