Conspiracy theories never achieve the status of greatness unless some fabulous mythology surrounds them. Mythology can come from adding on locations where a conspiracy of one allegedly occurred. Government myths are essential for any good government conspiracy theory. Religious mythology is always handy for ancient and secretive groups. Finally, myths that come from pseudo science or faulty logic are great conspiracy enhancers.
The tale of a woman who exits a shopping center, store or building, gets into her car and is shocked to find that a murderer/psychopath/homeless person hiding in the back, has been located in Wichita, Kansas, Los Angeles, California and numerous other places. This is a conspiracy-by-one urban tale that, in reality, may have led others to try the same trick for real, but in many locations.
The first greatest government conspiracy alleges that the government is all powerful and can control the hundreds or thousands who work for decades on an ultra top secret project to the point where nothing gets out into the public realm. The mythology is that the government will kill, disappear, permanently sequester or otherwise make an example of anyone who leaks information. This is highly unlikely, if not impossible. Someone associated with such activity is going to talk in their lifetime. The government cannot control all who have ever worked in a place of ultimate secrecy. The reality is that once a person leaves their position, most government missions change and reorganizations can be so massive that a person's recollections can become meaningless after even a few years.
The fact that many ex scientists, soldiers, civilians and contractors say little or nothing adds fuel to the mythology of ultimate government control. The competing fact that their jobs might have been dreadfully boring, or that the individuals have self discipline is less appealing.
The second government great conspiracy alleges that places like Area 51 and Area 52 are monstrous underground complexes that contain everything from shelter for the world's elites to alien civilizations, with a host of individual conspiracies piling on. First of all, these are not conspiracies! These are ultra top secret programs.The mythology is that any government operations that are in such complete secrecy can automatically be assumed to be evil, corrupted, too much for humanity to handle, or horrific in their nature.
The fact that no one has come up with much verifiable information about those places adds fuel to the mythology of government evil and power. Another fact, that the vast majority of workers are in mundane support positions that get nowhere near the "good stuff" is frequently ignored.
Whenever a great conspiracy involving ancient and secretive groups such as the Masons, Catholic orders, Jewish groups, Original Nazis and so on, a religious or anti-religious motive and power comes around. The group can be accused of everything from being agents of Satan, Gods, and other mythical powers, to being evil operatives of the organized arms of the great religions. The older the group and the more generations who have served in the groups, the more credence is given to the myths (many of them equally ancient) that there is some super human, supernatural or divine force that protects or continues their existence.
Pseudo science, Religious and quasi-intellectual thought:
The Biedermier Group is accused of being a shadowy cabal of the world's richest elites, who have a goal of killing off all but half a million humans. The conspiracies that are attributed to the group involve various mad scientist or megalomaniac trains of thought, combined with the resources to carry out diabolical and global threats. Religious and secular mythologies that foretell or prognosticate the end of humanity or the end of the Earth often are applied to inaccessible, enormously wealthy and hugely powerful groups.