First off I'm not really sure what we would call
劝ing in English, it's not really exhorting or admonishing as dictionaries would lead people to believe - it's more like actively sticking your nose where it doesn't belong to tell people, who don't really care, what to do.
Moral propaganda encourages people to 劝一劝. Complete strangers will approach you on the street to 劝 you.
So what's the deal?
Why is 劝ing so common and popular?