The people in charge just don't care. For instance, newly declassified government files on UFOs seen in the UK from 1985 to 2007 reveal that the Ministry of Defense (the MOD, which is the equivalent of our Pentagon) didn't make much effort to investigate the strange sightings that kept being reported.
BBC News quotes National Archives consultant David Clarke as saying, "One of the most interesting documents in the files is a piece from an intelligence officer, who basically says that despite thousands of reports that they've received since the Second World War, they've never done any study or spent any money or time on the subject, and they say that people just won't believe that when they find out."
The files show that a man named Alex Birch photographed images of what looked like a "flying saucer" over the town hall in Nottinghamshire and sent them to the MOD in July of 2004. The agency's report said "no definitive conclusions" could be made from the photos. In one of the files, ex-flight controller Freddie Wimbledon describes seeing a fighter plane intercept a UFO seen both on radar and by people on the ground at a military airport. He says the UFO latched onto the fighter plane on the ground, "following its every move" before departing at "terrific speed."
Retired MOD official Ralph Noyes describes being shown footage of UFOs taken from the fighter aircraft. Another file reveals that MOD "experts" concluded that sightings of lights in the sky in the summer of 2006 were Chinese lanterns, which is reminiscent of the "flares" explanation in the Phoenix Lights sightings, as well as similar sightings throughout history (NOTE: Subscribers can still listen to this show).
One person who DID care enough to disclose what happened to him is Whitley Strieber, who wrote several books about his experiences--both as an adult and as a child--and his famous book Communion, with the alien "face" on the cover, is now available from the Whitley Strieber Collection, complete with an autographed bookplate!