I'm from Mexico. The first time I heard that word from a professor in a master's degree seminar (back in 2004), I asked him for an explanation. What he told me was that the adjective "societal" is formed for the conjuntion of 'society' and 'total' in order to mean the society as a whole, as a system, relating to the structure, organization, or functioning of society, what seems to have certain logic.