On blockchains, your identity isn't just controlled by your key. It's controlled by a program. That program can grant access to a particular key, but it can also encode a backup mechanism: as long as three of five of your closest friends vouch for you, you can add a new key.
Decentralization doesn't mean no one's in charge. It means you get to choose who's in charge, and there's zero barrier to replacing someone you put in charge.
What sort of programs do you expect people to actually write/use?
This seems sort of like saying, "If you switch to OpenID, you can run your own provider on your own website." Wonderful, but in practice people use some third-party OpenID provider. (A couple people might run a static website with the appropriate link-rel tags, so they keep control of the name but they're still delegating the actual auth work to a third party.)
Is the standard program going to be to grant access to a key + 3-of-5 friends? How do you enroll if you don't yet have 5 friends on the system?
The most popular identity programs in the early days will have no backup or centralized backup. As more people establish identities, decentralized backups will be more feasible.
As the ecosystem iterates on identity programs, we'll converge on secure, reliable, decentralized backups.
Decentralization doesn't mean no one's in charge. It means you get to choose who's in charge, and there's zero barrier to replacing someone you put in charge.