Alien conspirarcy theories worked as a baseline test for the CIA to track how effective propoganda and misinformation is before they rolled out the same techniques in places that it mattered for US foriegn policy interests.
I should say, this is mostly speculation based on reading a lot of COINTELPRO and MKULTRA stuff, it seems likely a way to test obsfoucating military technology through misinformation.
Furthermore if you notice the global UFO reported sightings, it seems to only line up with where American media has a hegemony, which is strange considering China has nearly 2 billion people in it, you'd think one of them might have seen one; it seems to only be where american media has reach that 'UFOs' start to appear and I dont think thats an accident.