At the risk of getting into another history discussion and getting told off by modmins, I'd say it had more to do with the complete air-superiority of the Allies, and the general lack of everything for the Germans. They could have had all the fuel in the world, the Battle of the Bulge was never going to work anyway.
But as to the greater point, yeah, fuel is pretty damn vital. Modern tanks can go quite far, but Ukraine is big. At the end of the day logistics is the most important part of warfare.