Big pages go private when they are doing a SFS....I will let you guess why.
Going private will help them track which shoutout gained them more followers.
How exactly does that help?
If the user has 1000 requests in his queue after a shoutout going private doesn't help trace where they came from.
If anything, going private will damage a shoutout as some of that traffic will visit your profile, see you're private and not bother following you.
I'd be interested to hear your thoughts on this...