It seems as though virtually all seforim (especially those written by Acharonim and earlier) refer to G-d as either Hakodosh Boruch Hu or Ribono Shel Olom, and never as "Hashem." Similarly, I don't think I've ever come across a single instance of G-d being referred to as Hashem in the Talmud or Midrash.
Is this because "Hashem" is a relatively modern term? If so, who came up with it, and when did it start becoming normative?
If not, is there some reason why HKBH and RSO are the preferred terms in rabbinic writings?