Simple answer: bad logistics.
More complex answer: No matter the superior performing technology, and the superior experience and tactics, the Germans lacked the production capacity to defeat the combined forces of all the Allies. Couple that with a gradual whittling away of their industrial capabilities due to Allied bombing raids, and a gradual loss of territory from which to draw labor, natural resources, and manufacturing, and you get a military that simply cannot sustain itself.
The German strategy for fighting the war at an operational level relied on a certain level of arrogance and belief in the ultimate superiority of German forces. Yes, your Tiger tank is a badass tank, but it's expensive and complex to produce, it takes longer to reach the field, it's harder to operate and thus harder to train crews to use, etc. Thus, you have a very small (comparatively speaking) number of really awesome tanks going up against a huge number of fair to quite good tanks (IE: Shermans, Cromwells, T-34s).
While superior ability and technology CAN win the day, you need to have a technological superiority far beyond what the Germans had. They had the edge, but they didn't have ENOUGH of an edge to rely on their technology and tactics alone.
Don't believe me? Try playing Orel, driving a single tiger tank around. Now go up against a Soviet team of 6 players in their T-34/76s. Sure, in a one-on-one duel you'll dominate at pretty much any range. But you can't be everywhere at once. Game over. You lose. Allies win. So much for superior technology.