Answer:
Because even if the free market system is the most efficient economic system that humanity has found, it sill can produce some undesirable effects for society that need government intervention in order to be corrected.
Step-by-step explanation:
For example, in the free market, if a company is more efficient than its competitors, it can become a monopoly, and monopolies affect consumers because they can set prices higher than normal.
Also, in a free market economy, even if many goods and services are produced, and both output and income rise, some people will still be left behind in poverty. It is a socially desirable thing to help the poor in order to keep society more harmonious and just.