Because the 2nd hand valuation is so much lower than the purchase price, there aren't any sellers. There's TONS of demand to get a diamond for 80% off retail,

Because the 2nd hand valuation is so much lower than the purchase price, there aren't any sellers. There's TONS of demand to get a diamond for 80% off retail, but many diamond owners would rather not sell than accept the massive write-down on their "asset".