The original minhag of Ashkenazim was not to say morid hatal and ain k'elokeinu. In Eretz Yisrael it became the custom to say them because the Chassidim said them as part of Nusach Sfarad, and the Vilna Gaon also held of it and the non-Chassishe Ashkenazim were primarily his disciples. The Rema writes the reason not to say ain k'elokeinu/ketores was out of concern one would skip words in his haste to rush out of shul to work, which is akin to making ketores without all the ingredients which is liable death. This reasoning is not universally accepted, see Mishna Berura.
It is an old minhag not to say Birkas Kohanim in chutz l'aretz and the Poskim are troubled by the rationale. The common reason given is because it must be said joyously, and out of Eretz Yisrael people were too preoccupied with parnassa to be relaxed and happy. In Eretz Yisrael the basic Halacha is followed. While attempts were made to institute Birkas Kohanim in chutz l'aretz over the centuries, no one ever succeeded in changing the established minhag.