There aren't many things about the past that need to come back. The Plague, as a safe example. Sometimes certain sayings are lost just because they aren't relevant to everyday life, or they refer to some person or story that isn't popular anymore. Some sayings are lost before they get to live out their full potential, and these ones look like they've still got some juice in em. Some popular sayings are total bastardizations of their original meanings, this tumblr thread explains.