Some people are try-hards and like the attention that comes from private blogs.
Our private blog is actually made for a reason, because we are from the All Nighter's Club and we wanted to talk more about sex so we created the blog so we won't have to worry about anyone reporting.
Because they're private. So you have to be on the person's friend list most likely to view it (or if you are on their ignore list and they have the settings where people on the ignore can't see your blog, that could be a reason too)