In the early 1930s the Russians were evaluating a lot of military stuff and basically settled on "well, given these advantages it makes the most sense to not try too hard to specifically prevent our territory from being invaded, just let it happen and then with the help of a winter unlike anything in most of Europe slowly crush them on our home turf with our manpower advantage." And that's exactly how WW2 turned out. Sure they botched the start of it and lost more men and territory than they were expecting but they basically did the obvious thing. Hitler just thought he would be able to take all the strategic assets in the West of Russia, capture Moscow and force surrender before that happened. He was wrong. Just like everyone else who's invaded Russia.