It is so well preserved, because those who were liberated from it, were so horrified at what they witnesses, that they did not want anyone to forget. It was a herculean effort, many wanted to bury it,because of the pain, and many more wanted to bury it, like it never happened.
A personal salute to all those who fought to preserve it.
There is a great video on the Poles who worked to preserve it. A lot of it is ... Unspeakable.