I still recall peak copper prices back in 2011 and all kinds of analysts saying they would go even higher. 

China was under pressure because inflation was running rampant and low-income families were quickly unable to afford basics, like groceries. There was growing talk about the possibility of revolution. So the Chinese government announced that it planned to restructure the country's economy to become more consumer-oriented, not just a processor/manufacturer based on raw materials. 

Copper prices went through the floor and CUU's long period of dormancy ensued. 

That may be a bit of an oversimplification of how events transpired, but I believe it encapsulates that period of history rather accurately.

Anyway, I sure hope we don't see any sort of repeat of those events in 2021.