Why are the soviets to blame for a German massacre?

Oh yeah the massacre with polish bodies that misteriously popped up right on the borders with the USSR and where reported by nazi german soldiers and immediatly used by propaganda by the nazi goverments. Also why those reddit assholes cant see that even if the soviets did this massacre, why would they let the bodies so close to the borders that german soldiers would see? Nobody does this shit, its basically giving propaganda fuel for your enemy. Its so obvious the nazis did it and planted the bodies on the soviet border to create propaganda.

Because this is the absolute cornerstone of russophobia and anticommunism in Poland. If that fall, entire construct will get very heavy blow. This is the reason it is completely impossible to hear any conflicting message in Poland, and anyone who is trying to dig deeper than official propaganda is immediately labeled "stalinist" "conspiracy theorist" "insane" and even "traitor".

For comparison: in official polish lore even things like Volhynia massacre and Holocaust are forgiven now. But Katyn... never. Also, it's not even the only one thing falsely attributed to the Soviets, there is also the intelligentsia extermination carried by nazis, which is rarily even mentioned now, and Soviets gets accused of it, with some time-space spin apparently.