The whole thing about flat earthers is that they come up with more and more elaborate explanations to fit each individual observation, when Occam's razor says that the theory that explains them all should probably be the correct one.

Like, they'll argue about refraction of light due to hot air being the cause for the disappearance of ships past the horizon, and then their explanation for how time zones work is something else entirely, and why we have seasons, and why planes take the routes they do, and all this other nonsense. They all need separate, complicated explanations, and they willingly accept them and vehemently deny the simplest theory that ties everything together.

The actual explanation for this behaviour is flat earthers are a friend group, doubly so for the people who pushed "globeheads" out of their life. So to change their view is to socially isolate themselves