they don't have the engine and maneuverability to reach that speed. if they had, you'd have to have the same kind of logistic and complexity as a fighter craft, negating most of the above points about drones.
missiles don't have the same restrictions because they don't have to have anything in the way of performance as loiter time or target search system or payloads.
what you're thinking of are Anti Radiation missiles such as https://en.wikipedia.org/wiki/R-27_(air-to-air_missile)
but that ties with the point being made originally, you have to sacrifice payload, or go bigger to have more payload options, or go sideway and have air superiority drones sweep the area before, and it all ties into the "this stuff hasn't been tested in symmetric warfare so who knows" argument.
