It's not mainly about the facilities provided by the universities, or the faculty it has. The repute of IBA, LUMS, and to lesser extent CBM and LSE is mainly because of the difficulty to enter into them due to relatively hard admission test. IBA teachers are one of the worst (I've heard they have improved the faculty now), and their facilities/teachig material/style is still very outdated as compared to let's say CBM, Iqra, Szabist or Bahria. But still it is the preferred choice in Karachi market mainly due to the fact that just after doing Inter or A levels, all the bright (and not so bright) students prepare to get admission in IBA and LUMS as their 1st choice.
This is definitely not the case with QuaideAzam uni. It may be huge with great facilities and faculty, but I have heard very few bright students, if any at all, that could not pass the admission test of Quaid e Azam university for BBA/MBA. The quality of students coming out of the university is what really dictate the institution's reputation in the job market and the quality of students going in them in the first place is obviously the biggest factor in that regard.