I believe the intent is that you're not supposed to be trolling or parked inside the airport except in the staging area. If you're legally parked outside the airport and get a ping, there's nothing they can do about that. I doubt Uber or Lyft are doing anything special with pings inside the airports. If you're parked outside the airport and get one, it's likely you were just the closest driver. I haven't looked to see where the staging area is, but I bet if you could find an off-site location that happened to be closer to a terminal than the staging area you'd get the ping every time.