Large corporations could easily gain monopolies in their field. A monopoly is when one corporation controls all or most of a certain aspect. For example, if you were the only person to sell lemonade on a hot day, you would have a monopoly in the lemonade business. You'd be able to charge however much you wanted for your lemonade because there would be no competition.
Large corporations were more powerful than small businesses. Due to this, they could easily make more money.