The money he puts up is not a down payment on the underlying contract, but a performance bond. The actual value of the contract is only exchanged on those rare occasions when delivery takes place. Moreover the commodity futures investor is not charged interest on the difference between the margin and the full contract value. In general, futures are harder to trade on inside information. Commission charges on futures trades are small compared to other investments, and the investor pays them after the position is liquidated.
Most commodity markets are very broad and liquid.
Transactions can be completed quickly, lowering the risk of adverse market moves between the time of the decision to trade and the trade's execution.