Mostly they only had a limited window to sac Moscow before Russia could muster all of their resources to stop the nazis. Originally it was predicted aftert the initial invasion of the nazis into russia that Moscow would fall in about a month, but supply lines and holdups in areas like stalingrad delayed them too long so they couldn't take out the Soviet hq before reinforcements arrived
I'm not a student of that chapter of history, but the picture I got was that nobody was prepared for how incredibly cold Russian winter actually was.
edit: and that same story played out several times in modern history, as I understand it. Don't send yer guys to the Russian front in windbreakers and t-shirts. The only people who successfully kicked Russian ass in that cold fucking weather were the Finns, not a warmongering culture, but they can definitely do what needs to be done in chest-high show at 20 below zero, because they're used to it.
Stupid. NAZIs could have and would have made new axles that fit Russian tracks if it were a big issue deal maker or breaker. I guess you imagine otherwise? Like the Germans couldn't fabricate axles that size? And that's why they lost WW2? The explosives raining down from the sky and the entirety of the Western World shooting bullets at their soldiers had nothing to do with it? Or just a side-issue?