After all this time, no answers. Theories, and usually those are presented as "THE" theory. A one time, one size fits all offering. Naturally, those theories don't work. So we're back to it.
But the classics still hold. Keel, Vallee, among them and many more. While I still think that some UFOs are literal spaceships from other planets (within our own solar system) there remains a huge part of the UFO phenomenon that doesn't fit that opinion. And that's the part that many find frustrating; what is it? Why does it do what it does? How does it fit in with … just about everything?
Well, as to "why" we don't know. Though it seems obvious "they" enjoy playing games, and maybe that's the why. That simple. Great joker, trickster, mind games playing energies that perform and contradict just for the hell of it. There's no great mystical "why" just that they're inter dimensional assholes. Or, maybe not, of course. Some say their performances are to wake us up -- that implies an altruistic agenda on their part.