Wartime spending was the subsidy. It always kickstarts the economy although it also changes several industries that are retooled for the war effort.

There is no such thing as a completely free market. There are constant regulations and oversight by government to provide a fair and stable environment to conduct business. When that changes, government again steps in to restore the balance. Again, it's there to serve the people. What exactly is the benefit of letting everything fail and plunging the country into another depression?