The internet is decentralized. It is literally millions of computers all around the world, no central point of failure. Google, Amazon and Facebook do not control the internet, if that is the extent of your internet usage, I feel sorry that you are missing out on so much more. If those companies were gone tomorrow, the internet would be just fine.
Bitcoin is decentralized, with many nodes holding a copy of the blockchain, no central point of failure.
By your logic, you may as well call it centralized since it only available in one galaxy, so if you can spread to more galaxies, then it will be more decentralized lol.
Internet is centralized when a government can cut your access or limit it. It is centralized when you're paying your ISP for the ability to connect to the web.
It is centralized because somebody owns the cables. Those fiberoptics did not produce and lay themselves. Your local network at work is also centralized because someone owns the computers and someone pays the bills.