Because it's an example you can use to explain a forward contract, which is easily understandable. Vast amounts of the value of crops are hedged, either through forwards, futures or derivatives. Crops aren't destroyed because of futures contracts. Indeed, the whole point is to ensure you don't need to, because you've hedged the value of your crop.

I get where you're coming from, and there's a lot which is not great in farming, but hedging values isn't one of those areas.