Flat Earth was a manufactured and amplified conspiracy theory that gained prevalence. Media loved talking about Republican Christians that believed it. Like Q, it was used as "look at how retarded conservatives are." It was a timely tactic to sully the weaker minds and make them more inclined to discount people speaking against the narrative (Wu Flu, election, Biden's acuity and China connections). That isn't to say that there aren't people that believe FE, because there are, but the media can take a handful of idiots and make them seem Legion.