Or, because you and the rest have been convinced that they're rare and hard to get. Truth is, there's billions and kazillions of them. They come out of the ground if you dig in the right spot. Heck, there's more gold in Saudi Arabia than water.
No, gold is genuinely rare, unlike diamonds. We can even make more perfect diamonds than mother nature can, but they are still expensive because there is a public perception they should be. Women want to wear 2 months of a man's salary around their finger, just to show how rich their husband is.