The Internet (TCP/IP, from the 1970s) and the Web (HTTP, HTML, from the 1990s) are designed to be decentralized.
A lot of work went into technological decentralization but there was little focus on the accompanying social and economic aspects. The social and economic dynamics have then led to massive centralization, and as Sir Tim Berners-Lee notes:
The web has evolved into an engine of inequity and division, swayed by powerful forces who use it for their own agendas.
The effort to correct this is known as redecentralization, and the vision as the Decentralized Web, or dweb for short.