I very much dislike copper as being seen as a precious metal.
The original penny was a big chunk of copper.
So valuable that there was even a half penny.
But today, with modern mining, you can buy tons of copper for not much money (in investing terms) and this pulls a big chunk of the necessary metal off the market. Driving prices up, and making many manufacturers deal with less than they desire.
And then, the inevitable happens and the person has to sell their copper. This floods the market with a bunch of metal leaving no real buyers for the freshly mined stuff.
The "investing" in copper really messes with the market and sends bad signals to the miners about demand. Copper mining is a very slow process, and messing with the market so quick.
At least with gold, there is so little real use for the metal, so locking it up in vaults, although we have mined more than we will ever need, it can just sit there.