Money is power--it commands not only goods and services in private markets, but also the services of those who govern. Only those who control large corporations can provide the money politicians need to campaign for national office in the world's largest economy.
So, in a capitalist political system, the primary role of government is to nurture a private market that will in turn subordinate government to the profits of the wealthy minority who control large corporations.
Why would any society want to do this? Ask our two political parties.