Why are there so many books, movie, documentaries, etc. about the Holocoust? Why do we keep retelling this story?

To tell you the truth, I not very sure that there is many things that talk about holocaust and also I not very sure that they are repeating. If there is then it is trying to tell us to do something or telling us to do what to do for that is what we should do and that is the right thing to do. So it want us to learn more and more about it.