How cam somebody deny it?

It happened about 60 yers ago. 6 million people were murdered. Why? because of their religion. Their crime was the fact that they were jews.
Today is the national day for remebering the holocaust in my country. I can't believe people actualy took part in killing other people, for no real reason, just beacuase their leader told them to hate and kill innocent people.

So many communities were simply deleted, by the proccesed murder. Children cried but were not helped. Elderleys prayed for it to be stopped, but no one listen.

I am a 17 years old teenager, and I live in Israel . My family from my mom side- except for my two grandmothers- were all killed in the holocaust.

The one thing I truly do not understand is why people try to deny it happened. Why in some of the most developed countries in the world, this entire part of History is being taken out- and forgotten. It's not okay. it's not right. We all must remember what happened, and remeber to not go back on those mistakes. How can you deny an historical event that has so many proves? concentration camps, Camps of annihilation, testimonies of both surviviors and children of the generals of the camps. With so many evidences, how can you say my people made up a story (to just get some mercy)?

I beg you, don't forget the holocaust. This is the only way we can be sure such crime as this will not happen again.