Except they aren't testing (solely) in developing countries; this test and whatever anomaly ensued took place in Arizona. Not exactly the population center of the US, granted, but the tests are being done here at home.
Facebook isn't alone in this regard, either, as Google has its own fleet of experimental drones. N749G flew over my house in the Memphis suburbs last Monday night enroute from KSIK to KOLV. The FAA says it's an "Ashfloyd Hummingbird," whose manufacturer has essentially zero public presence, but the model has been tied to Google's Project Wing. I kinda wish they'd keep their testing a little more remote.