@betterdeadthanreddit@lemmy.world The Soviets had joined up with the Nazis; they only "switched" because the Nazis didn't want them anymore. Then, after the switch they got busy wasting their soldiers' lives because what's the difference we've got more, and the soldiers got busy committing war crimes. Then once the war was over the Soviets repaid a lot of the surviving soldiers by sending them to the Gulag.
Also, as a side note, the communists in Germany who had helped splinter the left and hand power to Hitler, who had by then adopted a hard line pro-Stalinist platform and were trying to save Germany from the liberals by enacting communism and aligning with the USSR because communism is the answer, generally got executed by the USSR if they managed to make it out alive. Stalin killed a higher percentage of their leadership than Hitler had, and also assisted Hitler in killing a bunch of the German ones before the war, because of course he did.
Not to say the non-Soviet allies had any short supply of war crimes against their enemies either, but there was a massive difference of kind and degree, and they at least mostly were good to their friends. There is a reason that everyone in Europe at that time and after the war was risking their lives, their fortunes, and their sacred honor to get as far west as they could manage.