Commodities prices move higher and lower for a myriad of reasons. Supply and demand fundamentals are the microeconomic rationale for price appreciation and depreciation. Each raw material market has idiosyncratic factors when it comes to production and consumption.
The weather and natural disasters can also cause prices to move.
However, the asset class trends higher or lower together at times on the back of macroeconomic factors. The United States is the world's leading economy, and the dollar is the reserve currency of choice for most central banks. The dollar is also the benchmark pricing mechanism