Comment: Missy here is a shot at an answer

Corporations as they grow will seek to expand their influence to grow their profits.

In a free market the best way they can do that is by providing better and less expensive products and services.

If they do that consumers will vote with their money and continue to purchase the goods and services from companies that best satisfy their needs.

The problem comes in when companies realize they can use the profits they have made to influence government to get subsidies, bailouts, preferential tax treatment, protective tariffs, favorable legislation that operates to squeeze out smaller competitors etc.

The result here is companies start to make their money not because they are serving the customers best but because the government is now an ally in helping them maintain their profitable position. In turn the companies in exchange for the political favors donate to politicians' campaign ensuring that the politicians maintain THEIR positions.

The solution: Shrink the size of government, slash regulation, eliminate subsidies, bailouts etc. If you do that companies won't have anywhere to go to produce profits other than to the customer. If they don't do a good job a competitor will take their place.

Big government is not the answer to big corporations- at that point you have two leviathans working against you.