Wherever there's people believing in absurdities there is a big business opportunity, and I would dare to say that nobody among those who make money out of this conspiracy theory actually believe the Earth is flat. They're just milking the cow.

The problem is: what if they one day add some mystic nonsense to their theory, morph into a cult, then become more powerful until they can "purchase" a religion status? Sounds familiar? It may seem stretched, but assuming they're there for the money, the above steps would be natural moves to gain more power, immunity etc.