Because...

1. 2/3rds of the trucks that moved troops, supplies and armor were American made. A sizable chunk of the railway cars too.
2. They used far more American tanks and aircraft than propaganda would have you believe. Soviet former tankers who used both in combat preferred the Sherman E8 over the T34. Some of their top aces flew American P-39's.
3. At least half their own casualties, and perhaps more, were their own fault for poor tactics and training, zampolit (political officer) incompetency and forced ideology over military judgement, and Stalin's monumentally stupid orders.
4. Oh yeah, those trucks and tanks and planes ran on US fuel and their troops marched in US-made boots.
5. A good portion of their tank production used US steel.

I could go on. Without us, the Soviets collapse.

That, and OP should go look up just how much war materiel the USSR received through Lend-Lease.

They absolutely could not have survived the war they helped start, had it not been for US support.

Because German military logistics depended on over a million horses and they assaulted the USSR in the winter?

Yeehaw!

because we wish they had lost more.  if WWII had ended with Hitler and Stalin exhausting all their armies and all their resources and each finally killing his "socialist brother" in a fit of rage because their utopian dreams didn't work as planned, it would have been one of the greatest turning points in humanity.  If they could have taken all their minions and fellow travelers in the US, UK, Canada, etc with them, all the better.

This.

Which made the Moltov -Ribbentroff Treaty all the more mind blowing to the world and then the partition of Poland in 1939 between the Nazis & Soviets.

Both nations (Hitler's Germany & Stalin's Russia) were monsters who had zero hesitation to jail or kill anyone who stood in their way.

There were enemies in every fiber of their beings - Mongoose & Cobra who at some point would fight to determine which theology (Communism or Nazism) would prevail.

Bigger_Hammer

Don't forget that there was another "socialist brother" in the form of FDR and his entire administration. FDR desperately wanted to be dictator with unlimited power. He desperately wanted the USSR to own eastern Europe. He desperately wanted Germany to be reduced to a agricultural society. He desperately wanted to be king.

For that matter, he desperately wanted Japan to attack Pearl Harbor so that he would get into the war against Germany, and put Japan on the back burner.

The difference was that Hitler wasn't quiet as paranoid. He didn't decimate his own officer corp with purges.

I saw that FDR biopic:

Over 40% of axis resources were used in the air war over western europe.  Most of the Luftwaffe was focused over europe allowing the russians to have air superiority in the east.  The air war was clearly a second front before and after D day.  The western allies had nothing to be ashamed of.

They ate U.S. food in a very large part too.    Canned meat, cheese, oils, grain for their bread.

FPNI

Russia didn’t beat Germany, the US beat both Germany and Russia. Sure we had help from our allie’s, but it was our production that won the war. Both Brezhnev and Khrushchev said Russia was beat and if it wasn’t for US aid (pre lend/lease) then lend/lease they would have collapsed. What people don’t understand or were taught we gave Russia, planes, clothes, weapons, trucks, food, fuel, trains, we even sent a complete tire plant over. We gave them raw materials, steel the actual list of what was sent is absolutely insane.

Because the vast majority of the their industrial base was made possible by the US.  Especially their logistical base.

1.  The German war machine was trained inside the Soviet Union in the 1920's in contravention of the Treaty of Versailles in exchange for technology and training.

Kama Tank School

Lipetsk fighter pilot school

Tomka gas test site

2.  The Soviet Union entered into The Molotov–Ribbentrop Pact, officially the Treaty of Non-Aggression between Germany and the Union of Soviet Socialist Republics, which coordinated the invasion fo Poland by both Germany and the Soviet Union.  This invasion of Poland was the proximate cause of World War II in Europe.

3.  In the course of the Soviet Union's invasion of Poland forces of the Soviet Union committed mass executions and war crimes.

[url=https://en.wikipedia.org/wiki/Katyn_massacre]The Katyn massacre[a] was a series of mass executions of nearly 22,000 Polish military officers and intelligentsia prisoners of war carried out by the Soviet Union, specifically the NKVD ("People's Commissariat for Internal Affairs", the Soviet secret police) in April and May 1940.[/url]

4.  The Soviet Union waged an aggressive war of expansion against Finland.

The Winter War was a war between the Soviet Union and Finland. It began with a Soviet invasion of Finland on 30 November 1939, three months after the outbreak of World War II, ...

5.  The Soviet Union could not have fed itself, much less successfully prosecuted a war against the invading Germans without extensive material aid in the formm of Lend-Lease.

6.  The all-around shitty behavior of the Soviet occupying forces in Germany.  Much rape and looting.

7.  The all-around shitty behavior of the Soviet Union post war - Iron Curtain, Berlin air lift.