In general/basics/origins, farmers only want to sell futures, because they actually have (intend to have) the commodity for physical delivery, and do want to physically deliver it.
So who is on the buy-side? Exclusively supermarkets/distributors, while exclusively farmers sell? I suppose that could work, but I assume it would quickly regress into tight relationships like we have (probably regionally variable) for smaller market's, like most vegetables (vs grain) where as I understand it it's largely a direct relationship with the buyer - you probably still sell a future contract, but it's not via a central market and it is 'farm x will deliver to buyer y', i.e. a pre-order if you will, not really a commodity.
And as others say, price discovery, liquidity. What harm does completely open (no obligation) do? And maybe you eat a lot of potatoes and want to lock in the price today. (Or more seriously maybe you're a big baker, but not big enough to be buying direct from farm, your miller is. So grain price affects you, but ypu can't directly control/choose when to take it. Secondary grain futures allow you to hedge risk of it moving against you. In turn this means lower prices or lower risk of shock price increase to your consumers.)
Farmer agrees to sell an agricultural commodity to a grocer, for a price fixed now, with delivery after the harvest. Assume price falls a lot, and then the grocer goes bust. Ouch! Then the farmer must instead sell on the open market, at the lower price, and so becomes unable to make the payments on the mortgage on the tractor. Ouch ouch!
The farmer did want the price certainty that allows the risk of being more leveraged (tractor mortgage). But the farmer was not the optimal person to hold the credit risk of the grocer.
And the farmer might have sold without the intent to deliver. It might be that the delivery specification, or location, or whatever, isn’t perfect for the farmer. But if the farmer is confident that the prices will move together, then it still works.
So who is on the buy-side? Exclusively supermarkets/distributors, while exclusively farmers sell? I suppose that could work, but I assume it would quickly regress into tight relationships like we have (probably regionally variable) for smaller market's, like most vegetables (vs grain) where as I understand it it's largely a direct relationship with the buyer - you probably still sell a future contract, but it's not via a central market and it is 'farm x will deliver to buyer y', i.e. a pre-order if you will, not really a commodity.
And as others say, price discovery, liquidity. What harm does completely open (no obligation) do? And maybe you eat a lot of potatoes and want to lock in the price today. (Or more seriously maybe you're a big baker, but not big enough to be buying direct from farm, your miller is. So grain price affects you, but ypu can't directly control/choose when to take it. Secondary grain futures allow you to hedge risk of it moving against you. In turn this means lower prices or lower risk of shock price increase to your consumers.)