"does anyone have a clue as to why this is illegal?" TLC
Use of electronic devises for monitoring or aircraft for spotting then hunting is pretty much established as an unfair advantage in hunting. 'Guess common sense is not so common.
If your place is as large as some Montana ranches and you shoot an elk twenty miles from where your camera is set up, likely you won't have a problem. However, if your camera is set up on your twenty acres and you shoot an elk there, then it's hard to make a case that the camera was not a factor.
As far as private property hunting ethics, I think the following quote says it clearly.
Aldo Leopold: “ Ethical behavior is doing the right thing when no one else is watching-