True enough but we're not talking about civilians. We're talking about the military and most field armies were highly mechanized. As noted above, your logistics has to keep pace with your front-line forces, and that goes both for advance and retreat. It was extremely naiive of the German Army to think it could subsist to such a degree on horse-drawn logistics chains.
What I meant was that cars and trucks were not mass transport. Until they became mass transport you do not have hard top roads. We are all familiar with pictures of the German Army stranded in mud, but the British army was in the same position in 1914/18 and they built railways to supply the trenches. Tracked Vehicles cannot drive to Moscow from Germany and 1930s trucks get stuck in mud. The design brief of the 1934 Citroen 2CV car included being able to be driven on unmade roads and ploughed fields.