There were really thousands of Soviet composers, and thus gaps in the recorded repertoire are inevitable.
I hope you'll excuse an anecdotal remark made by Rostropovich on that point? :)
"Life was, in fact, very easy for a young composer in those days in the USSR. One only had to go to the Cultural Committee and say one intended to write a grand oratorio entitled "Lenin In A Hut"... and - whoosh! - they gave you a cash advance for the work, and year to complete it. How could they possibly refuse? So composers spent eleven months spending the fee, and then a final month writing the oratorio. On the due date, they took the manuscript to the House of Composers, and collected the balance of the fee. The House of Composers then took the manuscript, and buried it in a cellar unperformed. I often wonder where all that sh*t is now?"I don't mean to imply by this that all missing or unrecorded work is inevitably poor-quality, of course. However there was certainly a volume of work 'churned-out to order' for prosaic need, and the lack of performances isn't always necessarily a sign of a suppressed or under-appreciated masterpiece ;)
I realise that we all know this anyhow, but it never hurts to remind ourselves that music in the USSR was subject to different usage policies, which were themselves inconsistently and randomly enforced. However, while some of the music from that era may 'fail' for us today, it may well have met its intentions - for example, to be 'accessible' to the proletariat - at the time it was written. Considering that the alternative might range from a salary downgrade through to being sent to foster musical culture in a remote Kazakh town with no plumbing, the composers of this stodgy fare can sometimes be excused our censure ;)