The USSR was profoundly multinational, and many of the Republics - most notably Russia itself - were, in turn, fractally multiethnic, consisting of many semi-autonomous ethno-national regions (this is why it was called the Russian Soviet _Federative_ Socialist Republic, and the Russian Federation today).
On top of the already complex ideological balancing act involved in managing so many distinctive national and ethnic identities, particularly along the periphery, there was the strong official Marxist internationalism, the idea of friendship among the proletariat of all nations, and of the Soviet Union as a superlative embodiment of this, etc.
With such ideological/rhetorical objectives in mind, whatever you may think of them, it is easy to see why it would be a problem to give any particular people a sense of preeminent victimhood or confer unto them some special recognition. It can lead to enhanced claims for special status or compensation from those people, as well as animate the grievances of other ethnicities who were the victims of Stalinist policies such as forced mass resettlement, or who lost disproportionate numbers in the war, or succumbed to famines and collectivisation of agriculture, etc. Besides that, the USSR lost an estimated 27 million soldiers and civilians fighting the Germans--people of all sorts of ethnicities, but of course to no small extent Russian-Slavic. A self-interested government would not wish to antagonise veterans or grieving families by creating the perception that the mantle of victimhood was being somehow disproportionately alloted to a particular group.
So, there was generally a political reluctance to cast any particular spotlight on the distinctive plight of Jews in WWII. Doubtless, some amount of inertial anti-Semitism and a suspicious view of Jews played a role too.