I wondered about the distinction between cliche and idiom as seen by EL&U.SE and posted a question on meta (https://english.meta.stackexchange.com/questions/7740/where-does-englishlanguage-se-draw-the-line-between-cliche-and-idiom?noredirect=1#comment31642_7740) seeking clarification on the matter.
My conclusion about the difference in general was that a cliche is an idiom that has to become so common as to have fallen out of favorable usage (and as such seems to be a matter of frequency rather than some defining characteristic.) A few other users responded indicating that seemed to be a reasonable way to describe the difference.
My question is why did a separate term (cliche) come into usage as a label to describe the subset of idioms that were overused and thus less favorable?
Note I'm not asking why cliche specifically, but why a term was coined at all.