Well, I think it is fairly obvious that a considerable majority of Russians decided sometime during 1942 that the Nazis were even worse (for them) than the Commies.
I've heard this described as "better our beasts than theirs."
In addition, the Commies had the tar scared out of them by their very near extinction during 1941 and lightened up on their people quite a bit. For instance, they loosened up the restrictions on the private plots of the peasants and even allowed conversion of some communes back to co-ops. They allowed the Church a lot more freedom, in the hope it would help rally the people to fight for the state.
It worked.
Of course.
But a lot of them feared the guns to their rear more than those to their front. The kommisar's pistol aimed at the back of your head (or at your loved ones) is a powerful motivator. The Soviet man made the greatest sacrifices of the war, but saw none of the fruit.