A 14-month-old boy is referred to orthopedic outpatient clinic by his pediatrician for evaluation of a positive Barlow test detected during a routine well-child visit. The child's parents report that he began walking at 16 months with a persistent limp on the left side. On examination, there is a 2 cm apparent leg length discrepancy (left shorter), limited left hip abduction (40 degrees), and a positive Trendelenburg sign. Ultrasound performed at 6 weeks of age was normal. Hip radiographs show an acetabular index of 35 degrees, femoral head lateral to Hilgenreiner's line, and absent or delayed ossification of the femoral head epiphysis. What is the most likely reason for the failure of earlier detection and why is the current presentation a critical point for intervention?