Also, because people crave money. It is more difficult to extract money from decentralized systems compared to centralized systems. Therefore centralized solutions often have more resources available to pay developers, marketeers and founders (and investors), which leads to increased work on the product and (hopefully) more users. It is easy to see how this would lead to a virtuous cycle where the centralized systems capture the majority of the market due to having vastly superior resources and the decentralized systems capture mostly those users and developers who care about things other than money (eg censorship resistance, etc).
Money is a form of power, sure. There are different forms of power as well, not all of which can (realistically) be bought. Try purchasing serious weaponry for example (let's say a dozen tanks or fighter jets) and you will quickly discover that money is not enough.