Sensors and radars take more space, power and weight. So the drone will need to be bigger and more expensive and before you know, you will probably end up with

Sensors and radars take more space, power and weight. So the drone will need to be bigger and more expensive and before you know, you will probably end up with something that looks and costs just like a normal jet fighter. The F-35 is $200M. The Global Hawk drone is about $50M already and that's without any weapons systems.