Why are people obsessed with flat earthers?

We had a flat-earther here a few years ago

https://boards.straightdope.com/t/article-june-25-2010-how-does-the-earth-s-rotation-affect-the-path-of-a-bullet/

Maybe he was kidding; he seemed like someone who had picked up a lot of lies about what the Earth being a sphere actually meant, and also had never experimented with a flashlight to see how shadows behave, but who was absurdly sure of himself.