Supply and demand is the generic reason for the price of anything.
What you should look for is the underlying reason - why is demand increasing/decreasing?
In gold's case, demand was high previously due to economic uncertainty and as people sought a safe haven. With relative economic stability, demand has normalized and hence decreased from previous highs.
Exactly true, when chinese was unstable more people invested in bitcoin from china, they actually don't want to lose their buying power by holding on to FIAT currency.