I know what you mean. I suspect that some "members" got too wordy or mouthy, and decided to hide from their past, so they could have a second chance to fit in.
Personally - I don't like annonimity in such a casual, friendly setting. I think we all benifit from knowing as much as possible about the friends we make here.
If you're hiding something ...... it must be something big. Seems weird to me.