A 48-year-old woman from Mumbai with a history of poorly controlled diabetes mellitus presents with a 5-month history of cough, hemoptysis, and weight loss. She was treated for pulmonary TB 3 years ago with standard DOTS and was declared cured. She now presents with recurrent TB. Sputum smear microscopy is positive (AFB 3+). Culture and DST reveal resistance to isoniazid, rifampicin, levofloxacin, and amikacin. What is the most likely reason for this pattern of drug resistance?