A 45-year-old man with a history of chronic alcohol use disorder presents to the emergency department with acute dyspnea, confusion, and severe metabolic acidosis (pH 7.15, HCO₃⁻ 12 mEq/L). Serum lactate is 9.2 mmol/L, and liver function tests show AST 180 U/L, ALT 95 U/L, and albumin 2.8 g/dL. The anion gap is 18. What is the primary biochemical reason lactate accumulates in this patient despite normal renal function?