It s not just an US thing. Russians were just that good at not leaking any possible info. That was kinda the point of the gulags in the first place, to seclude people that could say how much it sucked. But mainly their spy net was top notch at the time, really, adversing a just recently born american spy 'network'. Back then, it wasn t even a fair fight intelligence-wise.
While I could tell you I did study a lot about communism in high school, stuff like the Holodomor were grossly glossed over and a special emphasis was put on the nazi camps. Crossing concentration camps with literature is much easier to do than with the russian evil-doings, and nazi Germany is expected to be underlined on its every aspect as THE leading power over all WW2.... but i can definitely see why you would think WW2 russia doesn t get the attention it deserves in everyday history education.
To add to that i live in Italy, which had kind of a role into the whole thing, so that would most likely vary from other countries, though not that much from other european countries AFAIK