The Wehrmacht suffered from a number of logistical problems in Russia:
- Distance. The further it advanced the harder it became to sustain the armies. This is further complicated by distances between army groups.
- Roads. At times the Russian "road" network was little more than trails. It bore little resemblance to anything the Germans had encountered and certainly not on that scale. Additionally, they could not sustain the amount of traffic required. Periods of high precipitation and traffic volume reduced the roads to quagmires, further hindering logistical efforts.
- Volume. The further the log train traveled the more fuel, rations, and spare parts it required. This detracted from supplying the front which required more vehicles which used more parts, fuel, men and rations...now you have a circular problem.
- Rail. I think we can file the Soviet rail system under "LOL."
- Hubris. It didn't expect a protracted war, nor a winter war, and it showed.
- Fuel. In addition to hubris the Germans lacked the fuel reserves to sustain ANY war.
- Arrogance. Had Hitler allowed commanders to shorten their defensive lines it would reduce the manning requirements for those vast spaces plus the distances needed for resupply.
- Sheer numbers. As
@pardus pointed out, the number of available trucks and the number of troops to support them were out of proportion.
- Two fronts. Russia plus the desert and then later Russia plus Italy/ the Med divided German's meagre resources.
None of the above takes 1944 into consideration, but by then the war was "over" and not applicable to the crucial period from 1941-1943. The only hope Germany possessed was the quick capitulation of the Soviet Union and we all know that would never happen.