Not sure if this has been pointed out already but I imagine that at the time the decisions was made to refurbish the class 442 fleet, the refurbishment of the class 458 fleet was not an option as the introduction of the new class 701 replacement fleet was too far on the horizon. I understand that the delivery of 701s has been delayed.
Prior to the pandemic, the extra capacity was needed immediately and the class 442s in theory would have been a way to provide that capacity. Due to the prolonged duration of the pandemic, refurbished 458s are now an option although to my mind, they do not seem much younger than the 442 fleet. Maybe the ability to run as 4, 8 or 12 car units is the over-riding factor.