1- Our economy at that time was not so strong so we can not buy a new jet and bear its induction cost, training, infrastructure, maintenance facilities and tactics development.
2- We had AMRAAMs (a long awaiting weapons for BVR combat )and other advance equipment (New Radars, Sniper Pods, More powerful engines, and other up-gradation in avionics) with those F-16s.
3- Its operationally very easy to induct F-16s in PAF' s current doctrine.
4- Ground Crew and Pilots are familiar with this platform for quite long time.
5- PAF's Engineers and Technicians are trained to maintain this jet.
6- It also gave PAF an opportunity to upgrade their old fleet on same standard like 50.