Isn't the simple answer just Cold War propaganda, especially within education systems in the west? There was a strong incentive to minimize the USSR's accomplis

Isn't the simple answer just Cold War propaganda, especially within education systems in the west? There was a strong incentive to minimize the USSR's accomplishments and sacrifices in the west. Even if for some reason you think that the Soviets didn't have as much impact as people used to believe, it just means their propaganda was more effective earlier on. Either way, I think that's the easiest way to explain the change.