Here It Is Then

In the comments on the this post, Mark says: "That was easy. Please post more easy questions."

Fine. Then riddle me this:
We have thousands of chunks of garbage floating around in the sky, in orbit around earth. Some of which are designed and built specifically for detecting any sort of intruder which may attempt to breech our borders. Be it a missile [cough-cough]Star Wars[cough-cough], an asteroid, meteor or comet that may stray too close and move in for the kill, or maybe even a visitor from a galaxy far, far away.

On top of that, we have government entities monitoring for things such as a stray airplane, border jumpers, and other folks who may fly in under the radar.

So tell me. Why can't they determine whether or not there really was a flying saucer at O'Hare a couple days ago?