1. As is the case with most financial markets, when you place an order in the forex market, the trade is executed shortly afterward, but the settlement of trades - during which the trade details are entered into the books and records of the trading parties - typically occurs at a later time. Cash delivery is exceptional, because all of this happens in the same day.
2. Rather than physically deliver the underlying commodity or asset to the contract holder, it is much easier to simply transact the net cash value of the futures position instead. This allows investors to hedge against price changes in the underlying asset without having to worry about physically taking delivery.