Why do people reciprocate in their gift giving? Because of the resource curse: because a curse will befall those who hoard within the circle of circulating gifts.
The gift that is not reciprocated will bring upon its master a curse. The same God Who provided for so much bounty will cause the flow of abundance to dry up. He will stop the rains. The source of creative power will reciprocate in the negative unless the recipient of gifts reciprocates in the positive. If someone violates the justice of desert and keeps for himself the undeserved gift that another has bestowed upon him, the power of deservedness, of justice, will prevail and the hoarder will bring down upon himself retributive justice in the form of the withholding of what otherwise would have been deserved bounty.
The resource curse is the means by which karmic vengeance is meted out. It is not authoritative law that enforces payment for gift exchange, it is the higher authority Who keeps the accounts of justice in the world. It might well be that the worth of the gift could successfully be hoarded and kept to oneself and not given away but the meaning would wreak vengeance and undo the windfall of the hoarded gift's worth.
Some part of every gift is inalienable and cannot be given away. When something inalienable has been hoarded by another rather than being reciprocated or traditted, then a curse will revenge itself upon the one who violated the unwritten laws of gifted property.
Every gift has a soul of meaning, a hau, that demands its proper disposition and discharge. Things take on a spirit when they are offered as gifts. The spiritual center of our culture is embodied in the transformation of the material into the spiritual by the act of giving. Hoarded gifts have restless spirits that complain and cause disturbances within the domains of those who would violate the deservedness of such belongings.
Hoarding eliminates the spiritual from the culture. At a minimum hoarded gifts leave the hoarder with an inferior social status that can only be recovered when the gift is reciprocated. The sense of gratitude that comes to the undeserving by virtue of the granting of a gift by the deserving underlines the enchanting of society. That enchantment comes of the teeter-totter action of deserving and undeserving in the society.
Spirituality is the offspring of the sensation of desert. Gifts are wards that resist storage. Gifts must circulate. Sooner or later their wardens must send them away, else they rebuke their caretakers and revolt against them. The point of sending gifts on their way was to allow them eventually to return to those to whom they belonged, to their makers.
Soulless things can be exchanged; soulful things could only be gifted and ultimately returned to where and to whom they belong, to their makers.