Obviously, these people are being fed mind altering drugs by a secret government organization. Or this alternate theory from Skeptic Magazine could be correct.
Why do people believe in conspiracy theories? According to the University of Kent psychologists Michael J. Wood, Karen M. Douglas, and Robbie M. Sutton in a paper entitled “Dead and Alive: Beliefs in Contradictory Conspiracy Theories,” a conspiracy theory is “a proposed plot by powerful people or organizations working together in secret to accomplish some (usually sinister) goal” that is “notoriously resistant to falsification,”and that has ‘new layers of conspiracy being added to rationalize each new piece of disconfirming evidence.”
Once you believe that “one massive, sinister conspiracy could be successfully executed in near-perfect secrecy suggests that many such plots are possible.” With this cabalistic paradigm in place, conspiracies can become “the default explanation for any given event—a unitary, closed-off worldview in which beliefs come together in a mutually supportive network know n as a monological belief system.”