Probably because PIA flight wasn't due in till 01:00 and would have taken a couple of hours to turn around and would have required runway for take off at about 03:00 hrs - so the runway would have been unable to be worked on effectively for this whole period.
On the other hand the Jet2 was due in just after midnight then would be off the runway and out of the way for the night causing only minimal disruption to the contractors..