Nazis are a still a good screen enemy because they were very theatrical themselves, the uniforms look sinister and practically no one in the western world is sympathetic to them except a few white supremacists and no one cares what they think.The question you should be asking yourself is why Hollywood obsesses over the Nazis, a long-defeated enemy that will most likely never return to pose a threat to the world as we know it. My guess is that the powers-that-be use the Nazis, their legacy and anything they can attach to them as a weapon to beat the minds and consciousness of White people. And Inglorious Barsterds was nothing more than a Jewish revenge fantasy.
I hate to break it to you like this, but the United States wouldn't be the world's #1 superpower if it weren't for the technological advances they appropriated from the Nazis. Truman's administration conspicuously overlooked the undeniable atrocities and human suffering Nazi scientists, engineers and physicists had committed in the name of the Third Reich to profit from their knowledge and expertise.
Furthermore, at the time I doubt their enemies considered them "sinister" on account of their uniforms. You've just fallen for the Hollywood narrative, where they've associated the Nazi image with all things demonic and evil.