A 68-year-old man from Delhi presents with progressive painless dimness of vision in both eyes for 6 months. He has type 2 diabetes mellitus (HbA1c 8.2%) and hypertension. On examination, best-corrected visual acuity is 6/36 in both eyes. Slit-lamp examination reveals a mature cataract in both eyes with a brown nucleus. Intraocular pressure is 14 mmHg bilaterally. Fundus examination is not possible due to the density of the cataract. He undergoes phacoemulsification with in-the-bag IOL placement in the right eye. On postoperative day 1, vision is 6/9 with a clear cornea and well-centered IOL. However, the patient reports significant difficulty with near vision and complains that he needs reading glasses for all near work. What is the most likely reason for this postoperative refractive outcome?