I imagine that the reason might be that the world was still in shock over the Holocaust. Rabbi Miller's strong belief in Hashem, and that the Holocaust was punishment for a nation that the majority had thrown off the yoke of the Torah, was not the kind of talk that Survivors wanted to hear.
Yet time heals many wounds, and now we are in a better position to understand history the further removed we are from the events. The Tochacha clearly says what will happen if we forsake God, and Rabbi Miller is very clear on showing that a Jewish Reformation that originated in Germany, would be put to an end in Europe by the German people. RAM shows how assimilated the Jews had become, and how Hitler's YMSH first laws were promulgated primarily to force a separation between Jew and Gentile.
I understand that for survivors, this book will be a difficult read, but the general thesis, that it was a Divine Madness, is clearly explained in detail. The German people were the most academic, the most cultured, the most refined and modern people of the time. It could have only been a Divine Decree which turned them into killing fiends.
Although I don't really care too much for holocaust literature, (as I have unfortunately had my fill) this book was refreshing in that there are many chapters which detail the history of how the Jewish people from the time of Mendelssohn, moved from following the Rabbis and Roshei Yeshiva to following the Haskalists.
The footnotes are excellent and I recommend this book strongly for anyone interested in an eye-witness (RAM learned in Slobodka from 1932-38)account in what Europe was like prior to WWII. RAM claims that it is a "fairy tale" to think that pre-war Europe was a Gan Eden of learning. Most Jews did not keep Shabbos or attend Yeshiva, but had already migrated to the progressive schools.