It's been pretty clear for some time now for those who study the facts that there is a very good chance there are real objects in the sky that maneuver in ways that conventional aircraft are unable to and cannot be explained adequately as other observed phenomenon. The taboo around this subject due to the common hypothesis they are due to extraterrestrials is a shame because there's been plenty of documented evidence that not only has this been going on but that governments around the world take it seriously enough to investigate it.

I found this book to be a good take that avoids hyperbole and tries to stick to the evidence and facts:

https://www.amazon.com/UFOs-Generals-Pilots-Government-Offic...

If you were to ask me to guess, my bet is that current and past government programs to investigate these objects have concluded that a) they are non-threats to US national security and that b) performing further invasive means to investigate them past our current level of understanding is too risky to pursue. So (again if I had to guess) the consensus is, theories of their origin aside, "don't look into it further, and be assured that there will be no harm in not doing so," which is why you can see a program like this shut down without necessarily assuming that it was a waste or a wild goose chase.

If you are genuinely curious about officially documented reports about UFOs (not aliens), then I highly recommend reading "UFOs: Generals, Pilots, and Government Officials Go on the Record" by Leslie Kean.

http://www.amazon.com/UFOs-Generals-Pilots-Government-Offici...

In a field where many of the books are written by either true believers or debunkers, this is a fresh take on the phenomena, carefully researched and conservatively written by an investigative journalist.