Because if the monetary policy is expected, banks, brokers and other institutions that will be affected will make pre-adjustment. In the end, if the policy is really implemented, it will not achieve the expected results.

Although the expected fiscal policy will be affected, it cannot be said that it is completely ineffective. Because fiscal policy generally affects a wider audience than monetary policy. It's not that strong to want to adjust in advance. Moreover, the influence of fiscal policy is often more profound than that of monetary policy, and it is very difficult to completely adjust these influences. At the same time, fiscal policy includes some policies that can hardly be adjusted in advance, such as tax adjustment and price restriction.