In this video Contact 699 it is explained why a public landing of extraterrestrials did not take place.
In a comment James Moore asked : why the USA ?
I don't have a youtube account and i saw that nobody give the right answer.
In fact Ptaah answers this question from Billy in a contact (I don't remember which one).
That's because the United States has the world's largest communications network. This guarantees the maximum impact and audience for such an event.