I would say (2)
Long distances through the Russian steppes elongated the communication and
supply lines of the German Army requiring almost the same numbers of men to man
them as the ones to actually fight the war (most of them used to fight
partisans attacking supply lines). The harsh winters deteriorated even more
this situation disrupting mechanized and horse transportation and producing the
need of even more specialized goods (anti-freeze, furs, special clothes, etc.).