Dancing with the Fairies.
It is my impression that the Central Bank created computer digits are just not interested in PMs at the moment.
The Left (model making) Brain is more interested in models of Reality than any tangible reality like gold and silver.
Copper is more interesting as it is a good analogue of the real economy of things. It is used in all electrical appliances.
The correlation of gold and copper is probably caused by a third factor- everyones' obsession with representations of wealth. They are not interested in copper or gold as they are not esoteric enough.
Society and the economy are certifiably insane- they are off with the fairies. Think I exaggerate? Let us get a professionals opinion. Dr Iain McGilChrist at the Schumacher College.