The difference is that when you create a google account your user info is stored in a private database. In Satellite, the reasons for going through all the trouble of storing user IDs on Ethereum are 1) So account creation is permissionless 2) It's not possible for Satellite or anyone else to delete your ID and 3) Any application can read the data from the blockchain that links your name to your key.

Seems pretty decentralized to me. What am I missing?

What's the identity/signatures you mentioned for Satellite? It doesn't require an email address, for example, so what's associating an account to the actual real life me. Genuine question.