They did, which is why it seems like a relevant example to your question. They shipped centralized, and have already replaced the centralized service they shipped with a decentralized service.
Facebook messenger is not completely decentralized, but it is E2E encrypted now after years of struggle with governments and UX. It's definitely possible to move centralized systems to be more decentralized.
It's an example of somebody replacing a centralized protocol with a more decentralized one. It's also one of the biggest direct messaging platforms in the world with E2E encryption.
