First I have heard that we even had a stock futures market. During the long election night Fox mentioned that US stock futures had taken a serious dive, hundreds of points, as Trump's election victory became clearer and clearer as the night wore on. But, in the morning when the real stock market opened, everything was hunky dory, the Dow went up a couple a hundred points over the day.
Why do we have a futures market in stocks. Futures markets were invented for agricultural commodities, crops, which are in oversupply right after harvest, and become scarcer and scarcer as the once a year harvest gets used up. Used to be, if you were a farmer, you could get much better prices for your crop if you waited til well after harvest to sell it. Which takes money for the farmer to do. He has bills that have to be paid, and he needs the money from selling the crop. If said farmer has some cash in his checking account, he can wait, but few farmets have that much money in their checking accounts.
So, they invented futures markets. The producer makes a contract with the consumer to deliver a big load of crop, sometime in the future, at an agreed on price. And these contracts can be traded or sold, along with the crops. This smooths out crop prices over the year, which is a good thing for the producers. And as crop prices move up and down, futures contracts offer a way to bet on price movements. In fact the gambling angle proved so popular that futures markets in things that are not seasonal, like gasoline and jet fuel, were created. Southwest airlines was very good at playing the futures market in jet fuel and saved themselves a ton of money.
And, so, we now have a futures market in stocks. They are not seasonal, and the real stock market is open five days a week every week. Far as I can see, stock futures are just pure gambling. We ought to tax the hell out it.