It's because the political class in Pakistan is already a puppet in the hands of its Military. It's one of the few countries where the nuclear codes and strike decisions are in the hands of the military and not the civilian government. They control a puppet party which almost always gets a fixed number of seats from backward provinces. This party then becomes the king maker and hence controls who is at the helm of civilian government. The previous one (Imran Khan) also came into power with their support and so does the new one.