I personally understand it this way: selling interest rate futures contracts means that you think interest rates will fall in the future. Since the interest rate is expected to fall, according to the theory of rational capital chasing profits, depositors will naturally take out their deposits and invest in other places, or borrow at floating interest rates for investment, because in the future, when interest rates fall, there will be less interest to be repaid, while other factors remain unchanged, securities prices will rise.