The culprit is far from being mentioned. Everyone agrees that it is a stampede caused by deleveraging, and the value-preserving function of stock index futures urges institutions holding stocks to sell short to hedge the risk of stock decline. If the stock can't be sold, the stock index futures will be shorted to preserve the value, and the stock market will fall, forming a vicious circle. Looking at foreign bailouts, they are all bought together in the stock market and the stock index futures market. We only buy them in the stock market, and the effect is not good.

As for why it is restricted, because it is at the forefront of public opinion, it can only be broken to protect itself.