Compare to:
The true end will come when Pakistani nuclear weapons fall into the hands of the religious fanatics, who, undeterred by the doctine of mutually assured destruction, stage a nuclear terror attack against the US, Israel, India or any combination of the three. Then the literal end will truly come for Pakistan. What rises from the ashes will likely be a number of smaller nation states, each firmly under the control of the civilized world. A hard lesson will have been learned by all – that religious fanaticism must never be allowed to blossom again as it did in late 20th/early 21st century Pakistan. link
Put it all together and I think we have the answer to your question, Asim.
For "80%" of the Pakistani populace the purpose of having nukes isn't defense but to kill for emotional satisfaction. Pakistani leaders are aware that foreign leaders know this. Consequently the longer the range of Pakistan's missiles the more the hackles of foreign governments will rise - the more potential enemies Pakistan will needlessly create. It's only logical, then, that Pakistan not undertake to develop (at least openly) long-range missiles at all.
But covert development won't do much good, either. It's impossible for Pakistan to hide such things now with satellites from the U.S., Europe, India, and China scanning every inch. Look how OBL was caught, it took ten years because every house in the country was scanned and the home the CIA could
not say OBL wasn't in was the one finally targeted. Same for Iran, I guess.
So if a "bolt from the blue" strikes the affected nation (or its loyal allies?) will know the terrorists' home address. Do you think they will respond immediately in kind out of fear of encouraging such irresponsible behavior or will they be willing to hold back and talk nice?