Government actions are unpredictable.
The market hates unpredictability.
It is as if you spent a lot of time researching fast horses and good jockeys with an eye towards betting lots of money, but when you showed up to the races they announced that they had an official who would add or subtract from race times as he saw fit.
Still want to bet your money?
An interesting aside...in the period of the 1920’s through the 1940’s when socialism was really starting to get some traction, one of the big arguments they used to implement central management was that the free-market system (those eeevil capitalists) created an inherently unstable and unpredictable economic environment.
Their argument was that central management would eliminate that unpredictability and create an environment of expectations that could be relied upon.
History has proved that the greater the power of the central managers and the more they try to manage the more frequent the swings in all aspects of the economy and the more wild the swings.
Some would try to explain this as complicated, but it is actually quite simple.
When a handful of people try to dictate to millions what employment there will be, how much it will pay, how much manufacturing can produce, how much they can sell their goods and services for, they are trying to push with a rope. One little snag anywhere along that rope and it binds.
By allowing the market to drive the economy, millions of people pull the economy rope along, when there is a snag, legions jump in to fix that snag and keep the economy towing along.