Given the possibility that aliens have been seen as in the case of Chicago O'Hare Airport UFO sighting, Why haven't aliens made contact with us? Why all the secrecy? Are aliens afraid of us?

There have been many different occasions in different years, in various locations across the world where there have been reports of actual sightseeings of UFO. According to some of these reports, people without the influence of toxic substances have witnessed UFO’s.