TLDR: The spreading belief in the flat earth model, where it occurs in good faith, is a side effect of those in power taking steps to ensure public relations stays effective.
Full text: In my opinion the flat earth thing is a hybrid of trolling, entrepreneurship, and engineered vulnerability. The first two are clear, that last one needs some explanation.
Long story short the people that run earth do so via engineering various beliefs in others which are favorable to them. An easy example of that is someone promoting a faith they don’t share and then exploiting the faithful.
That has become a literal science, social psychology. what one could call applied social psychology is generally know as public relations, or propaganda. I would loosely define it as the science of using communications tactics to alter brain processes. Usually, but not limited to, emotions that lead to profitable behaviors in the target audience. Such as buying a product or service.
Now, this is a huge industry to put it mildly. I don’t want this to turn into a general post on public relations but that background is important. Just search Edward Bernays. I’ve written about him before and I comment about him constantly because he’s a great entry point to the subject.
In order for the fruits of that endeavor to persist, (and it is in the interests of the established leaders of society than they do) a certain fertility in the minds of average people must be cultivated. Efforts to maintain a spectrum of conditions under which public relations works best have I think inadvertently created a soil in which flat earth belief can flourish.
To combat it would require combating vulnerability to applied social psychology itself. So I predict it’s not going anywhere anytime soon.
If you want to understand the first wave of those efforts and how they were and are successful, I suggest you start here: http://underlore.com/the-tyranny-of-compulsory-schooling/