Couple of points:
1. The JF-17 was designed BEFORE the Ra'ad so a possible argument is that the Ra'ad should have been designed to be carried by the JF-17. This brings me to point 2.
2. An ALCM capability was needed for strategic purposes at all costs. I believe that the designers simply did not have the time, resources, and technology to design the perfect ALCM that is capable of being carried by all aircraft in PAF. They had limited time, resources, and technology and they did the best they could to give PAF a capability it lacked.
Now that that capability has been there for a while and has matured more things (such as SOW for JF-17) are coming online and I am reasonably certain that a smaller ALCM is in development.