To put what
@JamD is saying in economic terms:
If the Pakistani private sector can supply $2 b a year of arms to the military, that's a $2 b savings on our foreign currency each year.
So even if the exports are $100 m, the added economic value of the defence industry is $2.1 b because of the savings (from avoiding imports).
On top of that, because GHQ is spending $2 b locally, it is injecting $2 b a year into our economy, which leads to jobs in manufacturing, engineering, etc.
So you have a few million middle to upper-middle class households, which means they'll spend -- which means you'll get others investing to meet their needs.
Overall, that $2 b local arms purchase translates into $3-4 b of economic activity (because if the defence industry people need homes, the homebuilders need cars, and the car makers need food, and food makers need equipment, etc). The gov't will tax all that activity, so its revenues go up and, as a result, our defence budget goes up and we buy more arms locally.
That said, we might not do well with defence exports, but if our private sector can build capacity in engineering, high-tech manufacturing, and R&D, they could drive other types of exports. They can, for example, sell design and engineering services or join some giant OEM's (e.g., Boeing, Airbus, etc) supply chain.