Price volatility results in lots of trading, because there is money to be made in accurately anticipating the ups and downs. Also consumers of a commodity will want to hedge against high prices in the future, so they will be interested in buying futures contracts. For example airlines may (and have) invest in fuel futures to protect against large increases in fuel price.
Coffee is subject to great variations in supply (and so price) due to unpredictable weather. This causes the price to fluctuate a lot, so there is much interest in futures trading…both from actual consumers (wholesale level) and commodity speculators.
Iron deposits are found in almost every country, and so local issues have little effect on the global supply. This results in a fairly stable price, and so little incentive to speculate. There are lots of shuttered mines and recycling opportuninties that can be put back into production fairly quickly if the market price warrants, so even increases in demand don’t move the price a lot.
There’s only ten on the list, so something has to start at eleven.
As for gold, maybe that’s because gold isn’t just consumed for industrial uses, but held and then traded again. This could include that kind of gold, not just newly mined gold. So some gold could be counted again and again.
Not ones on the commodities market. But the securitization of mortgages that allowed them to be more easily traded on exchanges has a whole lot to do with it.