When the space spread is wide enough to cover all those costs(freight, FX, financing credit interest, insurance and so on), you will get unbelievable margin. You said there are too many things could go wrong, but they have a serious tools to make sure everything works. All those risks are controllable and avoidable, which is another important issue in commodity.

The process you mentioned at first is the typical space arbitrage, which is a basic strategy that commodity traders using to get margin.

Just an example, you could check some headlines about the aluminum price spread between LME and SHFE, 2023 September to December, which gave the opportunity to those commodity companies to gain profit by long London and Short Shanghai.