It isn't about physics or astronomy. The quote below from...

https://physicsworld.com/a/fighting-flat-earth-theory/

says it better than I can.

It would be easy to dismiss flat-Earthers as simply being misguided due to a lack of education. While there are indications that those susceptible to such views have low levels of scientific literacy, Landrum at Texas Tech says that flat-Earthers aren’t necessarily people who don’t believe in science. “It’s not really an education thing,” she says. “It really is about distrusting authorities and institutions. [It] seems to be based on both a conspiracy mentality and a deeply held belief that looks a lot like religiosity but isn’t necessarily specifically tied to a religion”.

Landrum thinks this conspiracy mentality is linked to science denial and a susceptibility to believing deceptive claims on social media (Politics and the Life Sciences 38 193). No longer the domain of a “foil-hat-wearing fringe”, she believes those with a conspiracy mentality have lost the ability to judge when to trust and when to be a sceptic. Their lack of trust in authority includes not just scientists but scientific bodies such as NASA, all of whom (they think) are part of a massive conspiracy to prevent the flat-Earth truth being revealed. “[They] view the world through this really dark filter where [they] assume that all authorities and institutions and corporations are just there to exploit you.”

Also, this from another article on the subject...

“With extraordinary few exceptions, no educated person in the history of Western Civilization from the third century B.C. onward believed that the Earth was flat,” historian Jeffrey Burton Russell noted in 1997. “A round Earth appears at least as early as the sixth century B.C. with Pythagoras, who was followed by Aristotle, Euclid, and Aristarchus, among others in observing that the earth was a sphere.”