Don't know, but one possibility is that the intelligence exists among us, ala Mac Tonnies. It would serve to keep us feeling secure and avoid panic to give the public the impression that this intelligence is something "out there" that pays a visit, and then leaves.
All governments would be totally impotent in the face of a permanent presence of powerful beings, what ever they are. I don't think, however, that they (what ever "they" are) would approach any government any more than they would approach any individual.
The government can't keep us safe against this one, what ever they're intentions. They can't control it - they won't even touch it with a ten foot pole.
This whacks of a conspiracy only in the sense that their denial, so complete as it is, suggests a fear of the phenonmon, and perhaps an intense yet secret interest in the subject.
One possibility is that we are being contacted by beings so far beyond or different than us, and we are in the beginning stages of this process, and they are still seeing if we are ready for them.
"It's life, Jim, but not as we know it." Bones
"There's a starman waiting in the sky, he'd like to come and meet us, but he thinks he'll blow our minds." David Bowie