That’s because “sexual liberation” is a myth propagated to gain social control; once that is secure sex becomes, for the subject class, a tightly controlled commodity, while for the Inner Party, it is doled out quietly as one of the perks of the nomenklatura.
While the Civil War was uncertain, the Bolsheviks were indeed the party of “sexual liberation.” Once Stalin had eliminated all opposition, the inevitable reaction ensued, with the remnants of the Russian family scattered across a smouldering, shellhole-pocked moral landscape.
You might give 1984 another read, focusing on Orwell’s analysis of the classic double-think of totalitarian regimes about sex.