Why do all krebs cycle reactions occur twice for each molecule of glucose that undergoes respiration?

The Krebs cycle reaction occurs twice because glucose produces two molecules of Pyruvate and then two acetyl CoA.

Explanation:

The citric acid cycle goes around twice for each molecule of glucose that enters cellular respiration because there are two pyruvates from the single glucose molecule and thus, two acetyl CoA is produced per glucose which is the starting molecule in the Krebs cycle.