Without wanting to get too far into a massive subject: it's important to keep in mind that invading the Soviet Union was a key Nazi goal. In their minds, the land and resources were needed to make Germany strong enough to stand against the British Empire and the United States. So what looks like a strategic mistake was really a key goal of the war for Nazi Germany.

Those military planners were probably right that they wouldn't get a better chance later... Which just goes to show how far their goals were from their ability to reach them. (A mistake not entirely unrelated to the whole "slavs are subhuman, Germans are superior" thing...)