according to two of my best friends , both of them survivors of the war, one in the Heer and the other in the Kreigsmarine, and both serving on the Ost front during Moscow, it was a matter of undersupplied and too lengthy supply lines. Items from Germany never arrived during the bitter cold months with the inclusion of non-winterized clothing which the Wehrmacht succumbed. Only after general mud in the spring was Germany able to bolster their men with needed materials and continue the advance elsewhere. it pays to have a fool of a leader in your midst