Why did they have diary's...

I think that one of the ways to get in touch with some one back in the day was by mail. One of the things that Anne was trying to do was writ about her days, in hiding in a small ass place. The one part were Anne talks about her mom beeing a smart ass, and the other bad or should I say making fun of her. In a book I think that they would keep all the good details out of the book, that's why I kind like the diary that Anne wrote....