Hitler considered Italians to be racially inferior to even the French. Also there was little cooperation between the axis powers. They didn't share much technology and or industrial power. Unlike the allies who were far more cooperative.

For example many people make a big deal about Hitler's plan for nuclear weapons... but what no one talks about is Japan's nuclear program... and how much closer they got to making a functioning nuke. There was very little information sharing between Japan and Germany, however.

In terms of industry, the Italian air force often had decent airframes but poor engines. The Germans had excellent engines but didn't do much to help the Italians with their air force logistical issues.

Take this in comparison to the US which absolutely flooded its allies with everything from cutlery to explosives to fuel and everything in-between. The Soviet army was bolstered greatly by American trucks, jeeps, and heavy machinery that would have made winning the war incredibly difficult.