If you believe in ghosts can you tell me this?

Believers say that ghosts are the spiritual remains of folks that were either murdered or died in an unfair or terrible way, and they haunt the world until their wrongs are righted.
So what about the 6 million Jews (and gypsies and homosexuals and the mentally unsound as well as many others) killed by the Nazis. Why aren’t we up to our necks in spectral Nazi victims? Hundreds of thousands of civilians and enemy soldiers were killed in horrible and unspeakable ways, but I don’t see much evidence for even a tenth of 6 million ghosts.