At least of the people who've been on the debates, the motive is quite clearly money. They all have apps, merch, blogs, or Youtube Channels they make money from.
Sure, you could say the same thing about most religious leaders. That doesn't necessarily mean that they don't sincerely believe what they're preaching. Flat-earth doesn't seem to me to be a particularly lucrative scam, the audience is too small. If money was really their primary motive I would think they'd find greener pastures elsewhere.