Because futures are leveraged in margin trading, when the margin is lower than 75% of the initial margin, the exchange will require investors to add margin, otherwise they will be forced to close their positions. This process of adding margin makes the loss of futures book become the actual loss of investors. On the other hand, if the futures are profitable before maturity, it will be reflected in the margin account in real time, and traders can close their positions without waiting for the futures to expire. It is precisely because of this trading mode of marking the market day by day and floating the profit and loss that the profit and loss of futures is the actual profit and loss.
Unlike futures, the rise and fall of stock price is only book profit and loss. You never know whether the stock price will turn over in the next second. Before traders sell stocks and get money, all the profits and losses are only reflected in the books, not the actual profits and losses.