In 1941 Russia actually had a few contracts going with Nazi Germany. Molotov-Ribbentrop pact rings a bell? Division of Poland? They had quite a few ties and political cooperation running. And until the end, right up until Germany invaded Russia, Russia upheld every single clause of that contract to letter and spirit.
That was, by the way, also the reason that the German army could advance so quickly in the first few months. Stalin simply didn't believe that they did that. They had contracts, they had pacts, they had agreements, they had basically agreed on a division of Europe. You get this, we get that.
Having something so intricate and complex simply ignored by who you thought of as your partner and being back stabbed does leave a mark. Russia was absolutely not prepared for this attack, and they will never, ever, be caught again with their pants down. Since that day Russia has never entered a contract without at least pondering what to do should the other side break it.
That's the reason for this. Once you understand that trauma, these things start to make sense, and I wouldn't put too much thought into it. They simply don't trust anyone anymore.