1) Germany defeated the Russians in WW I while fighting a 2 front war. The Germans were tactically superior and could not have been impressed by the Russian performance.
2) Stalin saw this and started forced industrialization and collectivization so this could not happen again. His reforms were brutal and immoral, but effective.
3) The Germans coveted more land.
4) Stalin gutted the Red Army officer corps with purges leaving the Soviets vulnerable.
5) Hitler ideologically hated the communists. He wrote in Mein Kampf that they needed to be exterminated.
6) By a combination of the 5 points above.....the Germans have motive and would rather fight SOONER than LATER.
As it turns out, the Russians were far more capable than Hitler realized. But we are looking back at history in hindsight. Hitler was thinking of the Russia that Germany beat in WWI.