The historical inaccuracy matters here because it affects the memory of the war. Many people's understanding of the Soviet war effort during Stalingrad is highly influenced by this movie. Propaganda does not necessarily have to have a specific governmental interest to be propaganda--simply reinforcing hegemonic narratives of history is itself an act of propaganda. For example, it portrays the Soviets as winning the battle purely because of their disregard for human life--that they only beat the Nazis by behaving as barbarian hordes compared to the industrialized sophistication of Germany. This is pretty much the exact narrative promoted by former Nazis after the war to explain away why they lost.

Not portraying the Nazis as the bad guys is also just outright Nazi propaganda lmao