Governments are fundamentally inept.
If we say that older angel and so on sightings were in fact UFOs, we could also say that present UFO sightings are actually misinterpreted angel sightings. How we see reality is too strongly affected by our beliefs, our conception of the world, our culture. We're all eager to believe evidence which proves us right. We're better off erring on the side of humility rather than that of ego-boosted importance. Too much of our individual realities is the product of individual perception.