Probably because the average person is retarded and bad at epistemology. Intelligent rational people will
converge on whatever the truth is because there's only one objective reality. But most people base their beliefs on whatever their in-group believes, whatever authority tells them, and whatever they personally want to be true. For example, religion. Most people only believe the religion they believe because they happened to be born into it. For things that require abstract thinking to understand, midwits and low IQ people lack the abstract thinking required to internalize them. For example, if you try to explain the concept of a bell curve distribution to a midwit, their response will often be something like "But what about this outlier?" as if that proves anything. Another factor is old people disagree with young people because of differences in neuroplasticity. Old people's brains are physically incapable of updating their beliefs anymore and learning anything new, which is why boomers are the way they are.