@ Bloddy clever
Depends on what that "better job" is. Being up in the air projecting noise all around, a flying vehicle close enough to provide recognition tends to be easily spotted from 360 degrees. It also has to exert quite a bit of fuel or energy to remain functional while something ground based can just sit there and transmit or wait till motion is detected.
Now consider going inside buildings. Odds are high a flying robot would either crash or be so large and slow to be both easily noticed and knocked down before it even managed to focus some recon pics.
In short the point of the strategic design was purpose specific robots. Sometimes flying is better. Sometimes not.