Germany is federalised much like the US is. It's basically run by the states, not the national Government. There are a few (BIG) exceptions that make it look different, but something like this absolutely falls into state jurisdiction. It's really just like a normal inheritance that you can reject in German law. If you do that, inheritance property becomes property of the state. In the case of a house, they will auction it off. In the case of copyright like this, they kept the copyright and let it rot in the deepest cellar they could find. For obvious reasons.
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Hum, make no mistake, many of them were absolutely in line with his racism and his arguments. Many were indoctrinated and brainwashed, and many all too happily let themselves be brainwashed. And not just few had the same ideas to begin with. Antisemitism was raging wildly in Europe at the time. Germans were not as evil as Hitler, but they were not innocent as a group either.
Of course, they did pay the price and attoned for it. Germans today are abhorred by what happened just like anybody else. And there's no guilt about it anymore. That dark chapter is truly closed by now. One of the reasons why republishing this book didn't cause that much of an upstir. Media tried but realised rather quickly that people simply didn't give a fuck about Hitler anymore. It's history, and history is boring to 90% of the people.