The Russian Population (190 MILLION) was so much larger than the German Population (76 MILLION). Especially if you add in other Eastern European Country's Belarus, Estonia, Latvia, Lithuania and Ukraine, that Germany had to occupy and defeat before facing Russia itself.
They did not have the Manpower to hold it along with Continental Europe. Hitlers plan according to some was to get most of the Eastern European and Russians to become conscripts to the Wehrmacht German Army. That would have worked If Hitler Did Not STARVE THEM TO DEATH Like Stalin was earlier before the War...
Then It Snowed...
End of story.
If Hitler was able to Feed the Masses, they would have flipped and attacked the Western Front in the Wehrmacht!
IMAGINE THAT BLOODBATH!!!!