A 52-year-old man with a 20-year history of chronic hepatitis C presents to the outpatient clinic with complaints of easy bruising and epistaxis for 2 months. On examination: hepatomegaly (4 cm), ascites, and multiple ecchymoses. Laboratory investigations reveal: Hemoglobin 9.8 g/dL, WBC 3.2 × 10⁹/L, platelets 45 × 10⁹/L, INR 2.1, albumin 2.8 g/dL. Peripheral blood smear shows target cells, macrocytes, and occasional nucleated RBCs. What is the most likely cause of the thrombocytopenia in this patient?