In addition to what everyone else has said: even if we did we wouldn't necessarily know what to look for. I have a friend who's PHD is trying to figure out what

In addition to what everyone else has said: even if we did we wouldn't necessarily know what to look for. I have a friend who's PHD is trying to figure out what ancient dams look like in order to find sites of ancient agriculture. But that's the thing "what does a 500 year old dam look like" is a lifetime worth of study and is only just now possible. "Just scan the fuck out of it and look for wierd stuff" is the dream but at the moment (as the other comments point out) we can't just scan everything but ALSO we don't know what's wierd.