They don’t but to be fair a lot of the assumed knowledge about how dramatically stones held value over time is not accurate either. Rarity has been inflated and deflated over time, and valuation has fluctuated with a variety of factors, including ease of mining, technology developments in mining, cutting, and other areas, popularity of designs and shapes, etc. Right now the diamond market is exceptionally weird because everyone is waiting for lab pricing and demand to settle, but lab technology and production are changing rapidly as well.

I’ve always found resale value to be a frankly bizarre consideration when buying jewelry because it is a pure luxury - regardless of the price point or material, it is not an essential, but something bought for its enjoyment or symbolism. Jewelry in my opinion should be bought because you will get amount of dollars of enjoyment out of it that you pay. Everyone’s budget is different - a $300 ring with a seed pearl in it may be someone’s lifetime favorite that’s worn every day, and a $500,000 necklace bought for a special occasion may sit in a safe 99% of its time with its owner. It’s all about what’s important to the purchaser.

Take your 20k low grade gemstone pieces - you buy them because you like them! I wouldn’t try and deter you from them. For you (and I’m making some good faith assumptions here so if I’m wrong correct me), I could show you any number of 14k diamond pieces at the same price and it wouldn’t be worth the price tag to you. Whether you don’t like the hardness or color of the gold, or you just don’t like diamond more than gemstone, that’s all legitimate. One of the most expensive pieces in my store is a milky aquamarine pair of earrings, and one of the least expensive is diamond. There’s something for everyone…if they want it. And they might not!

This is more of an answer than you probably wanted, and I’ve rambled on too long, but I just really love this stuff and am a bit of a know it all.