They’re not actually. Many UFO sightings are in broad daylight and sometimes by many people at the same time. There is a proliferation of UFO sightings in recent years. This has been explained by Dr Steven Greer of “The Disclosure Project”: For a long time the visitors from other worlds have been studying us and while we were no threat to other civilizations they kept a very low profile. Once we invented nuclear weapons and then ventured out into space they have been keeping a more watchfull eye on our activities.
They are not little green men that want to take over our planet but at the same time they don't want us interferring with theirs. They are more technologically advanced than us and more spiritually advanced than us (That's not hard!).
Our scientists are looking ever deeper into space and see more and more planets in the Goldylocks zone.(i.e. not too hot and not too cold, just right for life similar to our own). With the estimated millions of planets that appear to be in this zone where carbon based lifeforms are possible, the chance that we are alone in the universe is becoming closer to zero the more we look.
A simple search of UFO websites will reveal a ton of material some of which will be questionable but the bulk of it appears to point to an actual phenomena and not merely the wishfull thinking of children and bored adults. There are many youtube vids that show multiples of bright dots moving accross the sky all independent of each other. There's too many vids like this to count.
And 'Crop Circles"; I haven't heard any plausible explanations for the production of these mysterious and increasingly complex patterns.
The writer of the article in question had already started with the assumption that 'this UFO stuff is all a load of hooey'. Any serious investigator would have to admit that not everyone who has had some sort of encounter with something extraterrestrial was drunk, crazy, on drugs or a pathological liar.
Some people just don't like their little, easy, secure view of the world to be changed so are quick to pour cold water on anything out-of-the-ordinary. I believe that disclosure of visitors from other worlds is imminent.
Cheers