That's it. The People link/area on the sidebar contains links to a user's Profile page, but without registration there is no profile to display.
The main reason for wanting to see a user's profile is to send them an email, but without registration there is no address stored for them. Admins will see a few more details on a user's profile page but, again, all those details only appear once a user has registered.
Also, to appear on the People list a user must have posted. To prevent spamming almost all admins will set permissions so only registered users can post, so what you observe is rarely a problem.
Volunteer Helper - but recommending that users move off the platform!
Once the admin for GregHelp now deleted.