In Pre-Industrial Revolution societies, economic units are mostly small and local. There is a small, shipping based global economy driven by novelty items, managed by small businesses and, in the case of a major seafaring power/economic giant like Great Britain, the East India Trading Company. The East India Trading Company is one of the left fist of the British Empire, and although ostensibly a private business, was created and maintained by the government in order to secure economic dominance over foreign ventures. Such a large business would not be able to exist otherwise; there are no banks in the private sector that are willing to foot its loans or bad seasons. Only the government's revenue can do it. Also, no other institution can open its trade outlets the same way the government can (say, by subduing the nations of Asia). Naturally, the British government is entitled to a share of the Trading Company's wealth, which it obtains directly and indirectly.
In post-Industrial, modern economies, pretty much all corporations and small businesses -- the entire economy, really -- are in the position of the East India Trading Company. Businesses are only so large and successful as they become because the government is promoting infrastructure, order, and trade that enables a high level of growth. That takes money (in the U.S.'s case, the military is an important part of our economic growth), and most of the money belongs to the wealthy and to businesses.
So, they get taxed a lot.