That was with a total mobilization of their society (in 1941-45), with universal conscription and a call up of all its reserves. The Russian population now is much smaller than that of the USSR in 1941 (146 vs 195 million), and moreover it is much older. More important, the Russian government seems very reluctant to call up its reservists (those conscripts that have completed their service). Granted, it has never practiced calling up the reserves since the days of the USSR, and it doesn’t seem that its system is set up to do that anyway.
In addition to all that - they also had a certain industrial superpower supplying them in WW2.