Because the Germans emphatically did not fight alone. At peak, Germany counted Italy, Romania, Hungary, Bulgaria, and Finland as active military allies.

Case Blue, the 1942 operation which eventually devolved into the ruinous battle for Stalingrad, is an operative example. The Germans lacked the strength to prosecute the campaign on their own and so made use of large formations of Italian, Romanian, and Hungarian troops, mostly to protect the flanks of German units. Of the ten armies committed to the campaign, two were Romanian (3rd and 4th), one Hungarian (2nd), and one Italian (8th). These allied armies were generally less combat effective than their German counterparts for a variety of reasons (less heavy equipment, poor doctrine, etc) and in this particular case all were smashed to a greater or lesser extent by the subsequent Soviet counter-offensive (Operation Uranus), but they were certainly present.

The famed Afrika Korps (later Panzerarmee Afrika) in North Africa is another useful case. Popular history has largely written the Italian contribution out of the campaign, preferring to focus on the German formations involved. The Italians have often been portrayed as bumblers, just along for the ride. This isn't entirely surprising; the Germans from Rommel on down tended to hog the spotlight whilst simultaneously scapegoating the Italians for anything that went wrong, and this carried through into the postwar historiography. But in reality, Germans made up a relatively small portion of Rommel's forces, while the bulk of the army was filled out with Italian motorized and infantry divisions.

This is to say nothing of the hundreds of thousands of eastern "volunteers" who entered service with the German army and Waffen SS, either as combatants or as helpers (HiWis). These men ranged from dragooned prisoners to passionate anti-semites, and their combat performance varied from decent to downright horrible.