Like cultures and customs, the value of ivory depends upon the kingdom where it is seen.
In the Hyborian kingdoms, where elephants and other creatures are rare, it is a tangible sign of both wealth and power. In the Black Kingdoms, it is common - few warriors exist in those lands who do not possess an ivory handled dagger or jewelry.
It is a great source of trade between the north and the south - indeed it could be said that ivory is the primary reason that merchants dare make the dangerous journey along the Black Coast to trade for it in Kush.
The great herds of elephants which roam the Black Kingdoms are hunted daily for their tusks and there is no reason for men to suspect that the creatures will not continue to roam forever.