German logistics was unsuited for invading the Soviet Union because Germany wasn't rich enough in resources to spam out trucks and trains like the Americans could. People like to laugh at the Wehrmacht's logistics, but German logistics in the Battle of France performed extremely well. There were the inevitable issues, but at the end of the day they were able to sustain a high-intensity offensive campaign deep in enemy territory, which is pretty darned good when you consider that most of the burden was carried by horses. When it comes to invading the Soviet Union, having sufficient industrial capacity for satisfying both tactical and logistical needs is imperative, and Germany just wasn't rich enough to do it. Even if German logistics was well-managed, it would not have been up to the task.
It all comes back to German material scarcity, which is the very reason the operational level was prioritized so much higher than logistics; operational capability had to make up for logistical shortcomings because for Germany slow, methodical campaigns were unwinnable. The fundamental logistics of the country dictated that military logistics could never take first priority, whereas the wealth of the United States allows us to take the opposite approach.
Which was mostly due to three factors:
1) the campaign only lasted 6 weeks
2) they didn't need to advance that far
3) the good infrastructure in Belgium and France (for instance the panzer divisions could refuel at gasstations in France)
1) and 2) meant that it was exactly what the Wehrmacht (and German strategy) was prepared for. 3) meant that shortcomings could usually be compensated by living off the land. When these conditions weren't available, it fell apart (Barbarossa, North-Africa).
and even then German logistics squeaked a bit in France and those 6 weeks! Pazerschoclade and petrol run out a few times! (also the casualty rate and losses we're high)
That's what they needed to win, Hitler wouldn't accept that it was at best a long shot, telling Hitler no was unhealthy so they saw what they needed to see to please Hitler.
That's a bit unfair to Hitler* and a bit flattering to OKW/H in 1941
By the end of 1940 Hitler has just come off a wining streek of taking big risks and it working out going back to the invasion of Czechoslovakia and he's just topped it off with a stunning 8 week western campaign where he beats France and chases the UK off the continent, everyone and I mean
everyone at the time was stunned by that.
It is hard to overstate the significance of the fall of France here in the minds of those making decisions* in 1940-1941.
OKW didn't think they were going to beat France in 8 weeks, they were worried Hitler was going too soon in 1939 & 1940
But Germany (under Hitler and his decisions) has just done in 8 weeks what it couldn't do with the bulk of it forces and 4 years of trying in WW1, and that's the perspective German high command is looking at the invasion of the USSR with.
Put simply that perspective was if they can do the hard bit they couldn't do in WW1 in 8 weeks , how easy will it be to do the bit they could do in WW1 and beat the 'Slavic Untermensch'
There was no hidden reticence by OKW/H kept quiet by fear of Hitler in the run up to Barbarossa 1941, they'd have marched to the moon if he'd told them too!
*things I never thought I'd type today when I woke up this morning for 10pts!
**and I don't just mean In Germany the fall of France changes the war and perception of it completely for everyone.