This gives me Black Mirror-fueled nightmares... not least because those videos suggest that a Black Mirror scenario may not be that far off and what probably saves us for now is battery capacity.
These robots won't have any problems pulling the trigger at anyone or anything. They won't hesitate or refuse an order the way Stanislav Petrov did. They won't be trained to have empathy or respect for life. Humanity is the final check against the worst atrocities war demands from the people we send out to kill each other, and devices like these solve that "problem" by dehumanizing the soldier.
Come on man, this is delusional. I want to believe it too but be realistic.
Practically, because legs are superior to wheels when it comes to pursue a human target. It may be superior to flying as well indoor, to open doors, etc. And then there is the energy expenditure and additional mass constraint when airborne.
Research on legged robots is not just for 'fun', it's because they are better at going through obstacles and rough terrain than wheeled vehicles.
Flying can get you almost anywhere, but not quite. It is both very loud and has issues in enclosed spaces.
Wheels/tracks are very efficient at moving mass, but have issues crossing some materials such as exploded building internals like you would find in a war zone.
Walking/climbing is the last bit to get you inside enclosed 'human' spaces such as buildings and tunnels.
The war occurring now in Gaza would be an example area of what future battle would look like.... A target building it hit by a bomb and mostly destroyed. Smaller automated drones quickly fly over the area and assess visible targets and threats for follow up artillery. Multiple mobilized traced/wheeled heavily armored drones would address any residual ground level threats. Upon reaching the target building the larger drone vehicles would release multiple smaller 'walking/crawling' style drones to ascend the rubble, either addressing any remaining targets themselves, or reporting back to a command station for some other group to make a decision on what to do next. The final goal of these walking units is to probe deep into the rubble to ascertain if any tunnels survived the initial bombing, and if so to begin mapping any threats in said tunnels.
Personally,I think we'll get really good at killing robots and they'll get better at killing people (military).
If you watch it then those research legged robots will look rather more sinister... or maybe it's just me. That episode really stuck with me.