Conspiracy theories are planted by The Man. The Man is continuously engaged in fabricating and promulgating the most far-out yet tantalizingly-plausible-to-the-insane scenarios imaginable.
The responsibility for this function is located within the Marketing Dept of the National Security Agency, where a roomful of the most fiendishly creative minds this side of the Independent Spirit Awards work full time, carefully crafting plots and premises that are compellingly devious and reprehensible, while being almost impossible to conclusively prove or debunk. The resultant theories are then test-marketed via strategic plants in the conspiracy/political fanfic community and - if they show promise - are then put into wide release through the usual channels.
The purpose of all this is not merely to entertain. That is part of it, of course! The government does have a legitimate role in helping us, the general public, take our minds off the real problems that confront us and focus on something more fun. But that's not the real goal. The real goal is more sinister than that. These flamboyantly outré conspiracies are camouflage. They are designed to dazzle and distract from the perfectly mundane and far-more-far-reachingly devious conspiracies that actually are occurring. The real conspiracies. The everyday conspiracies - essential to the normal functioning of the government. The conspiracies you never, ever hear about.
You never hear about them, because real sneaking evil is far more boring in scope than say, spiking the nation's entire commercial jet fuel supply with mind-control agents so powerful that they work even when released into the upper atmosphere, in particles of parts per billion billion, every time a plane passes over. Despite the fact that we've yet to develop mind-control agents that produce reliable results even when administered in concentrated doses, at ground level.
See, those are the conspiracies that people love to worry about!
And our government provides them.