A 30-year-old female with a rare metabolic disorder is found to have a deficiency in lactate dehydrogenase (LDH), an enzyme that converts pyruvate to lactate. The physician explains that LDH specifically produces L-lactate, not D-lactate, due to its chiral specificity. What is the primary reason for lactate dehydrogenase (LDH) producing only L-lactate and not D-lactate?