IB charges $0.10 for each futures contract held overnight. It helps to maintain their 47% profit margin in their brokerage business.
"Carrying charges are applied for each net futures contract, net short call futures options, or net short put futures options on a single underlying for each calendar day the net futures position is held overnight."
We get double dinged with the carrying charge because the commodities account is a separate account for credit interest calculations with its own $10,000 balance for zero credit interest on cash.
Just appreciate your multiple contributions to IB's 47% profit margin.