If they were any good at it they'd be employed as journalists and win Pullitzer Prizes for their work. Nixon having his goons break into a hotel to steal information from his opposition is a hell of a "conspiracy theory". But we don't consider it that because Woodward and Bernstein put in the work to find the evidence.
Your typical internet conspiracy theorists are just plain lazy and very susceptible to selection bias. They make up things to fill in the gaps of their theories and refuse to change the made up bits even when they find evidence to the contrary. The general contrarianism of the internet pushes people to think the opposite of establish facts.
In the end it's just a mess of made up shit that conforms to the emotions of the person that made it up. These conspiracy theories are promoted among those with similar feelings. They push way more lies than anyone else.
On the internet, the first to make an accusation wins. If if the accusation is false, they still win. So even when they actually do the things they falsely accuse others of doing, they've already won the argument on the internet.
"You're just accusing us of doing what you did" is stronger than "You're now doing what you accused us of in the past" when the rhetoric is more important than the facts.