Why do people trade derivatives speculatively?

Why do people trade derivatives, such as furtures contracts on a single underlying asset, speculatively? Other than exploiting an arbitrage opportunity, I can see no logical explaination behind trading a derivative rather than just trading the underlying asset. Can someone please explain?

The main reason a futures contact exists is so producers of the underlying product can hedge their production & end-users can purchase future needs. Commodity prices would be VERY volatile if futures contracts didn't exist. Traders are just "allowed" to trade them for speculation which adds liquidity to the markets & creates a more efficient market but also creates prices that don't necessarily reflect the true supply/demand fundamentals. "Paper" supply/demand doesn't always match physical supply/demand.

When the "front month" contract nears expiration, speculative trading is restricted to closing positions only and traders move to the next "front month" contact. So when you say "trade the underlying asset", how do you trade corn, wheat, etc.... if you can't trade a futures contact? CFDs are a "fake" market based upon the futures market. The only price other than the futures market is the price @ the elevators which are not traded @ an exchange.