Equity trading is not zero sum. There are real businesses and assets behind the equities they represent that have actual value and produce actual money.
The same is not true for trading equities, they are not zero sum. There are dividends, buybacks, companies will sometimes spin off a part or parts as separate companies that you get newly issued shares of stock from (GE splitting into parts is a recent example), public companies get taken private at a premium to the market price, etc.
"I will buy y tons of corn from you in April for £x" - now I don't have to worry about how much my corn will cost and you don't have to worry about what your income will be.
These folks compete in a reasonably zero-sum game.