Alternative: There's no reason for my username to be public on the vast majority of sites/apps/crap that I use, so I'd rather just have a username, no password.

The secret username can be associated with a display name, real name, physical/email addresses, etc. You can use the latter to look up the former along with a password/probing question/ping (email, text, phone) to retrieve the former.

It seems to make more sense to me logically anyway: I'm not anonymously entering a secret club with a password. I'm identifying myself, and based on my identity I'm allowed to do something.