Competition compels them to produce goods people want, at prices people can afford to pay. Competitive markets harmonize individual self-interest with social good. According to Adam Smith, role of politics and government in the economy is minimal. Politics is broadly understood as struggles over social power and the future shape of social institutions.
Property is an institution which creates unequal social power.
The market is already implicitly political because it is based on unequal social power and because it affects the future shape of all other social institutions. Politics and economics are inseparable . Pretending that they are separate only hides the power which actually exists in the economy and prevents us from making it democratically accountable.