USA and Pak have an agreement in which they can only target those areas which are not under Pakistani Army control. Quetta is under Pakistani Army control but they fear turning Balochistan into another front.
CIA operatives can kill people around the world and they don't have anyone working for them in Quetta, that would be weird, no?
pakistan cannot seal its borders. It needs to deploy a million men to seal it off. Right now it only has 80,000 troops there.
Why do you need men to seal a border? Just put a fence and mines along the border.