A Times op-ed piece by Dara Horn blames the demise of standard transliterated spelling of Yiddish on the Nazis: "The only real difference between Webster's project and YIVO's is that, for six million devastating reasons, YIVO's failed and Webster's succeeded."
That seems to me an oversimplification. Even without the Holocaust, the number of Jews interested in reading Yiddish using English letters rather than Hebrew letters, or in reading Yiddish at all, would have diminished. American Jews just learned English, not Yiddish. Jews who went to the land of Israel learned Hebrew, not Yiddish, and if they wanted to learn Yiddish, they could have done so with Hebrew letters rather than by transliterating the Hebrew into English. And other Jews in Europe were assimilating and speaking German or Russian. So the population interested in a fastidious, standardized English transliteration of Yiddish is a small one indeed. That's not to diminish the substantial and indeed devastating role of the Holocaust on Yiddish culture, just to suggest that other trends and phenomena — Communism, Zionism, and assimilation and immigration — played roles that were also significant.