[compass_copium]

These systems aren't in place by accident. The US doesn't typically purchase roasted coffee beans or chocolate bars from South America either.

[cogman10]

Roasted coffee loses flavor after roasting.

Chocolate requires various ingredients to make that changes the characteristics of the chocolate. It also, famously, doesn't ship well.

Copper ingots, however, weigh less than copper ore and if they are actually too low quality they can be resmelted into a more pure level.

The only reason I can think of why you might actually want the ore is you also want and are extracting other secondary minerals.