Is preaching about something you do not really believe useless? why do people do this?

I guess alot of people are guilty of preaching cliches like "money is not everything" "beauty is the eyes of the beholder" "do not judge a book by it's cover". Why do a lot of people, myself include like to preach cliches we really do not believe? I do not know any person who would not reject an opportunity to getting a lot of money, date someone they really did not find attractive at all, or one person that does not judge someone by the way they look. So why are people so quick to correct others when they do those things and lecture?