Ideally, after the war is won, the propaganda activities of the victorious government would be gradually discontinued and the historians would be set free to pursue the historic truth (history is about discovering, disseminating and defending historic truth, after all).
Unfortunately, after the end of World War it did not happen – primarily due to a very urgent political necessity of denazification. Right after Nazi Germany signed the act of unconditional surrender (and thus effectively ceased to exist), victorious Allies were faced with a gargantuan task of transforming a thoroughly and deeply Nazi Germany (and Austria) into democratic and liberal nations.
Which, obviously, required applying a ruthless, powerful and omnipresent anti-Nazi propaganda for years (if not decades). Consequently, the Allies simply could not afford “academic freedom” in studies of Nazi Germany as the truth about the Third Reich (and the Allies) was capable of not only undermining the denazification project but killing it outright (especially given the outbreak of a new war – the Cold War).
In addition, there were historic facts that were very, very embarrassing to Western Allies (the USA, Great Britain and France). Armed robbery at Versailles that bore lion’s share of responsibility for the establishment of Nazi Germany and World War II; vital contribution of the West to the birth and maturity of the Soviet military-industrial monster (which made World War II inevitable); war crimes and crimes against humanity committed by the Allies in WW2 (and right after the war); the “Nuremberg farce”… etc., etc.
Consequently, for decades the Allies maintained – via funding and other means an iron grip on studies of Nazi Germany, essentially making it a propaganda endeavor – not genuine history. Obviously, in the Soviet Union and the Communist bloc nations the situation in historical sciences was far worse as every activity there was propaganda by law.
In addition, there was a powerful pressure from mass-media (that got so used to publishing anti-Nazi propaganda instead of truth that it had no desire to “change direction”).
And, obviously, from victims (first and foremost, from omnipresent Jewish organizations) for whom – for very obvious reasons – Nazi Germany was Absolute Evil.
No less obviously, this environment was not exactly friendly (actually, extremely hostile) to the honest and unbiased quest for historical truth. Worse, this extremely powerful external pressure forced historians of Nazi Germany to do something no genuine scientist (and yes, history is a science) should ever do – pass moral judgement.
It also cultivated powerful antipathy (i.e. negative emotions) towards the Nazis and powerful sympathy (i.e. positive emotions) towards the Allies. Powerful emotions that cloud judgement and thus create a grossly distorted picture of Nazi Germany.
And after the first generation of historians have been conditioned (i.e. transformed into anti-Nazi propagandists), it created a powerful peer pressure on the subsequent generations.
Consequently, it is very, very difficult for an academic historian (university professor, a fellow in a research institute, etc.) to “go against the flow” and search for the truth (i.e. genuine, objective and unbiased knowledge about Nazi Germany).
Hence, the only historians free to pursue historic truth about the Third Reich, are the “amateur” historians (i.e. not affiliated with any university or research institute).
In other words, historians who can not care less about peer pressure, pressure from the government, mass media, special interest groups, etc. Historians who work for the money – by selling their books and videos on the open market or pro bono – just to discover, disseminate (preach) and defend the truth about Nazi Germany. And for professional recognition (fame, if you will), of course.