That's how you end up with Google, Apple, and Facebook, Twitter, etc. They may start out as providing a service that works, but over time as they get bigger the incentive structure pushes them towards monetizing your data, locking you in, building boundaries around who can access what (e.g.Twitter APIs), and sharing data with parties you don't want to share it with.

One way to avoid this lock-in is to change the underlying incentive structure. That's what the blockchain does. The fundamental difference is not about centralized vs. decentralized, it's about the incentives that are a result of centralization vs decentralization.