With the Dissolution of the United Nations the only things connecting the human race were the universally recognizable corporate identities.
I could name the big ones, but I don't want to be sued. See image on the left.
Far more focused and stable than the various petty governments on Old Earth, they stepped up to take control of more and more aspects of people's lives, until everyone from the teachers in school to the guy cleaning the urinals had the corporate logo on their paycheques. Forget your local representative, instead seek out your local member of the board of directors.
When humanity ejaculated itself into the stars, they didn't just do it for kicks: they did it for profit. Whether it came in the form of a new planet to call home or a resource rich asteroid field, profit is profit. No one understood this better than the mega-corps.
But you have to spend money to make money, which is why the research and development budgets of every single company is always the largest red mark in their books.
The one way in which corporations failed to differ from traditional governments was their reliance on violence to get things done. Are your customers going to another company for their cheaper product? Send in the marines.