They focus on what is being taught in schools and colleges. First of all they are still following the traditional syllabus. Secondly, most of the grads don't finds maths as an interesting subject but they still study because they have to some how get through the phase either pre-graduation or the graduation itself. If we specifically talk about the post grads than they definitely opt. for the binary systems of numbers as there is a separate field (cryptography) associated with it, which is still in demand and can provide healthy income.
It is not only the study of prime numbers that is lagging in Pakistan - to seek an answer why, just look at this very short list:
1/ How did the country it's one and only Nobel laureate, and that too in physics (not that physics is more important than other branches, but that is the closest to prime number work amongst Nobel prizes).
2/ In a country where the majority is more worried about the after-life, what is there to make students want to study stuff that applies to _this_ life?! (I paraphrase a former prime minister of Singapore, https://azizakhmad.medium.com/the-singapore-story-74362fc3b389).
3/ Read any of the numerous very illuminating articles written by Dr. Pervaiz Hoodbhoy (https://en.wikipedia.org/wiki/Pervez_Hoodbhoy).