Granting your point that having more exposure is better than less, maybe the Pakistani players have just developed some really keen play styles that work really well against the unadapted.
You see similar things with Black players in the US. They are often isolated and hyper-competitive, and thus are over represented in the top tier based on population numbers.
Edit: Interesting. Why was this downvoted? Any competitive players here? I'm speaking from my own experience playing in US, South Korea, and Japan. Also, just take a look at the current rankings. For some reason, Tekken is huge in the Black American community.
Downvote all you'd like, but it doesn't change the facts: 3 of the top 6 professional Tekken players in the US are Black.
The frequency with which this sort of thing has happened suggests that, for some people, anything is preferable to the simple acceptance of the superior abilities of the people in question.
The fact you state in your final paragraph is consistent with a number of hypotheses, including simple chance.
American society has made a huge effort over the last 70 years insisting that deep down we are all the same and no group is inherently superior to any other. So when we see some group doing better than another group we need to explain it away as being due to some cultural phenomenon. Suggesting that a specific group of people does in fact have superior abilities is a very ugly thing.