It never fully left to need to be "reintroduced". It had only been a few decades since the revolution --- the scars of the old society don't dissipate that quickly and the struggle continues. As Lenin said a decade or two is a period of time so insignificant in the scheme of world history it is a trifle; and it is a serious theoretical error to measure political realities by the yardstick of world history. As well the war killed a lot of the most vigorous and energetic and politically dedicated youth who would have replaced them in the coming generations.

What Khrushchev did (on top of severing connections to the past which inherently breaks materialist continuity) was legitimize liberal ideology (dangerously doing so with a Marxist mask) and cease struggling against it, instead declaring victory, and as such undermining vigilance and diligence, allowing it to reassert itself without resistance --- or even knowledge half the time; after all, if socialism won in the USSR, why ruthlessly criticize all that exists including our own ethos?