You, yourself, know the answer very well. Policy making in Pakistan is mainly influenced by external factors and Arabic external are not so much strong to influence Pakistan's policy so, definitly, they are English. When the policy makers are English then you are familier with the consequences.

The other thing is tradition. We are very much sticky to the traditions whether those benefit or harm us. So, it is a trend in today's world to adopt English as your official language. You can take example of India, the so called progress of a small fraction of Indian population is due to their adoptation of English as their official language, it is useless to comment about rest of Indian population.
We, as a nation, are using same railways system, engines, tracks even signals today which were left by English government. Same is the situation in Education and Examination system. We have not adopted our own education & examination system yet but reforms in it. That'z why, these exams are in English.

I 'd like to add here that what we have changed and newly adopted is our enhanced Defense system and capabilities. Since creation of Pakistan it had been the main focus of every government, although it is necessary but other fields are styles of livelihood. That'z the reason, we are on top in Defense as we have number 1 Army and Intelligence of the world but we are on 163rd position among 180 countries regarding literacy rate. Same is the position of our Transparency and Accountability.

Hope, I have not bothered you.

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Fixed signs.