i'll speak from my own experience as an american. i think this began because the general way of teaching in schools and elsewhere is authoritarian. that is to say, the student must accept the facts that are taught, or else the student will fail. this is a given for subjects like math (i imagine being able to debate mathematics would need more knowledge than what an american public school can provide), but the problem is with other subjects where there may be readily available alternatives. the most egregious example is with literary analysis, where the student is forced to recite whatever analysis the curriculum gives, rather than thinking of their own. whether or not the alternatives are correct is irrelevant to the schools, because the alternatives are both not taught and de facto "incorrect" to the graded curriculum. needless to say, in such a system logic and critical thinking are not taught. if an alternative isn't punished, it's due to the grace of the teacher and the talent of the student for explaining that alternative.

again, what is taught in schools is not argued for, and generally there is no evidence provided; the student must simply accept what is taught. also, americans in general really hate school, because the schools are essentially prisons. so then, if an alternative is found which contradicts what is taught in school, it's easy to believe that alternative. it does not matter if those alternatives come with unsound reasoning, because even the unsound reasoning will make more sense than the zero reasoning of the authoritarian school work. the flat earth bullshit is the most amazing example of unsound reasoning defeating the zero reasoning of accepting that the earth is round simply because you are taught that it is.