While decentralized protocols don't entirely prevent centralization, they're still better than if the protocol was centralized. While Facebook and Google exist, we can still make websites. While most people use Gmail, we can still run our own mail servers.

Even if 90% of users use the centralized service, the protocol being open gives enormous value to the remaining 10%. And as long as the 10% keep the protocol open, the _possibility_ of decentralization can keep the centralized services honest.

We only need to keep the googles of the world from completely shutting down the open protocols. I mean, even that can get hard, but it's still entirely reasonable goall.