The Russians also won because Hitler was crazy- his master race doctrine and hatred of slavs prevented him from turning the Ukrainians against their hated overlords in Moscow.
The Russians also won because of the Strategic Bombing Campaign- American and British bombers, with little fighter protection, systematically destroyed Germany’s ability to wage war. Germany could neither repair nor replace tanks and planes lost on the eastern front because the factories that produced critical parts like ball bearings had been reduced to rubble. Fuel also became scarce.
The Russians also won because of the Battle of the Atlantic. American and British airmen and seamen kept the critical Murmansk shipping route open, despite German U-boats and bombers based in Norway, which kept the supplies flowing into Russia. Much of the Red Army often survived on Spam, which they called “Roosevelt Sausage”.
I forgot which historian said it best, but paraphrasing:
The Americans and British destroyed their steel, the Russians destroyed the flesh.