Why are UFOs only seen in the US?

What do you mean? Because it's a valid explanation. It's near impossible to fake a perfectly clear and high res, well focused image or video without showing artifacts of image manipulation. I do agree that a lot of those are taken in by amateurs on questionable gear, but I've yet to see a compelling video that cannot be debunked. And in the case of the navy or whatever army branch supposed sightings, I think those leave us with two options since they are so secretive on the subject ; it's purposefully deceptive or it's fabricated by third parties without consent. I want to believe but nothing ever comes out of those sightings so it's very hard to be impartial.