Corporate entities were radically more powerful in Teddy Roosevelt's day, far beyond what they are today. They were almost entirely unchained in regards to economic power, whereas today there is hyper regulation (tens of thousands of pages of it, including direct Fed control over the banking system).
Standard Oil was as powerful as the US Government in that era, as were the railroads. JP Morgan was far more powerful than the US Treasury. Cornelius Vanderbilt - pre Roosevelt - all by himself had greater financial capability at his peak than the US Government at the time.
The difference, is back then there was wide-spread and growing fear of the combinations and would-be monopolies. Today, Americans are relatively unconcerned by Microsoft (desktop), Google (search, android), Walmart & Amazon (retail), Intel (microprocessors), Facebook (social), Cisco, Boeing, etc.
