Why does this world need decentralization so much?

There are many plausible answers, but I will mostly focus on corruption in this small post. A centralized authority may make biased decisions in its own interest (or other's interest). We may take the example of the recent Facebook scandal: the company (the centralized authority) allowed personal data to be used in other people's interest. This does not happen only with companies, but also with governments - I believe each one can give an example from his/her country of recurring corruption acts.