Late to the party but I have a theory that makes societal a word that is redundant, yet made for a cognizable purpose.

Cold war affected political thinking much more in the U.S. than the U.K. - being one of the two superpowers that were the centers of gravity during the Cold War. While the USSR was "communist", another word that is used in similar contexts is "socialist". Thus, within the political lexicon, "socialist", and thereby, "social", becomes a dirty word. But, we still need a word to describe things having to do with society, without portraying them so negatively. Thus; societal. Explains why it came about only somewhat recently, though found to be in dictionaries at least forty years ago, mostly in the United States.