Or they're observed over military facilities because that's the only location with a rigorous surveillance system.
That this phenomenon appears specific to personnel and locations related to US military bases seems like an important piece of data.
https://en.wikipedia.org/wiki/Clutter_(radar)
Radar and infrared aren't infallible. The story of the pilot who saw something with his own peepers has my attention but I don't trust what they've only "seen" on instruments.
If I was an alien race sending probes far and wide I would absolutely focus my attention on hotspots of military presence rather than the relatively benign nature and civilian existence.