Answering the OP question: because it was a highly industrialized, rich country with probably the best organized army in the world. It could fight for so long because the level of "fat" (different kind of reserves, especially financial) the country had were large enough. In WW2 it had little fat and had to 1) conquer for resources and money, 2) collapse or 3) drop militarization entirely. So using risky and revolutionary military tactics was a must. The proof that they were risky can be seen by their enemies learning how to counter it by 1942-1943.
Also, the German's lost in 1918 because they were starving.
Starving soldiers don't fight well. And its well documented that the Michael Offensive stopped in part because the soldiers choose to loot food over continue the advance.
Moreover, the narrow window before the American's arrived forced Germany into a corner with very few strategic options. In addition, morale of both troops hinged entirely on the timing of American entry. If there is no American entry expected the Entente troops would have given up and the German troops would have kept on fighting.
American entry tipped the balance in the war (and its economic support kept the Entente from collapsing long before that). Without it the Entente loses. Period. Try to imagine 1918 with no American presence expected then or ever.
Which rather begs the question of why there weren't any reserves left (Flanders, presumably). You've also stated that that Gruppe Ruprecht were being pushed backwards continuously and didn't particularly get flustered by it - so why is Gallwitz's reaction so different? The combat power he's facing isn't so very different (more infantry, less artillery and armour).When Gallwitz started reacting to the US offensive (Meuse-Argonne), he was rather optimistic to teach the inexperienced 'Amis' a lesson. But they simply kept coming, despite blunders and losses. - And when Gallwitz eventually had to ask for reinforcements because his units were worn out, he was told there were none left. That started a series of retreats, which also affected neighbouring Army Group Crown Prince. In the end, Gallwitz was unable to prevent the AEF from crossing the Meuse.
The British and French were still attacking too, despite having taken broadly similar losses to the Germans. So putting the effect down to the US not having experienced heavy casualties seems simplistic to me.The Americans still had the 'spirit of 1914', i.e. they kept coming despite terrible losses. The Germans no longer had it. Already by early October 1918, simple soldiers were writing home that the end of the war was close. And risking once's life for a lost cause is kind of stupid.
OK, thanks - that's part of the history of the war I'm rather weak on.Gallwitz was perhaps more experienced than Rupprecht. He had fought two years on the Eastern Front, were manoeuvre was the rule. Then, he had been army commander at the Somme and at Verdun; and the units in AG Gallwitz were no worse than Rupprecht's or Wilhelm's.
Which rather begs the question of why there weren't any reserves left (Flanders, presumably). You've also stated that that Gruppe Ruprecht were being pushed backwards continuously and didn't particularly get flustered by it - so why is Gallwitz's reaction so different? The combat power he's facing isn't so very different (more infantry, less artillery and armour).
Starving soldiers don't fight well. And its well documented that the Michael Offensive stopped in part because the soldiers choose to loot food over continue the advance.