The premise breaks down when you think about it for maybe a half a second.
We found the camps. The Nazis were actively trying to destroy evidence of their crimes and cover it up. People who do things they don't want others to find out about, often do.
Like a dumbass congresswoman vaping and groping their date in a public venue, then denying it. Politicians and talking heads claiming a violent riot where the Capitol was breached was just "tourists visiting" for the day. Or Dipshit in Chief claiming anything unflattering, even direct quotes or videos of him, us "Fake News."
Or even things that are just unusual or hard to uncover. Like say, the USSR's bodycount! It's not like you found that up yourself, you are using government Numb3rs. Or are the government numbers only reliable when you use them for your points?
But the reason that people don't find the USSR's body count as reviled as the Nazi's is twofold. One, was they were our allies. Drawing a bunch of attention to it wasn't exactly what people wanted to do at the time. Two, it was mass death, not mass planned genocide. Like sure the Soviet government was responsible, but it's more "eh, well throw you in the gulags" or "Yeah, we're just not helping you with the famine" vs a concentrated effort to murder people. It's the intent that matters to make it worse in general, even though Stalin and the Soviets are... still well k own for being murderous monsters, so don't exactly get that protest.