If your identity is "simply" a public key, then...how does anyone actually refer to you? By a handle? That's not part of a public key. An avatar? I guess you could generate one à la Gravatar from a public key, but those aren't going to be very memorable.

A public key is a way to securely and uniquely say "this is me". It says nothing about who you are, anything about you, what you like or do, your links to other people, or anything like that.

All that information has to be stored somewhere.