Most centralized systems exist because the best way to extract profit from whatever they do is to maintain control. It's possible to profit from part of a decentralized system, but if you want to maximize your take then centralization is the way to go.

Every decentralized system that works was created with a goal other than directly profiting from it to start with, and succeeded because someone found a way to profit from some part of it. Eventually though, in most cases, the companies and people that run the system coalesce until its effectively centralized, with a few single entities running the points of failure. See electricity generation, car manufacturing, news media, game publishing, book publishing, glasses manufacturing, etc for examples. The Internet is still in the "companies coalesce" stage which is why it still looks decentralized, but those companies merge or vanish quite regularly, with fewer and fewer getting more and more control.