Because of the deliberate efforts of politicians (and the media and church figures who are involved in that politics), and the tribal arguments it creates.
In order to justify the continued power, authority, and excessive wealth of those who have it, they generate a series of arguments (even, conflicting arguments) to get people thinking they have a political argument with other “wrong” people that keeps them from noticing that the people telling them that are their rich powerful and/or “holy” “leaders”, who actually are only pretending they care about those same arguments so they can get everyone else’s attention off how there’s a class of corrupt super-wealthy assholes hogging all the wealth and power and telling them their problems are all about people in another tribe.
Particularly in modern US culture, you have many overwhelmed people who have little capacity for more information, and who would really like to trust one source of information, the simpler the better. Or even better, they’d like not to have to think about politics. So they’re eager to believe their choice of newscaster, preacher, politician or person they know.
Many US politicians and new media, conservatives and centrists have seemed to me to be engaged in social experiments to try to see how much BS and apathy they can get away with. Can we put an idiot in as POTUS? How about an actor? A reality TV star and con-man? Hey, look, we can! Can we have a lying right-wing news company or two broadcasting at a 4th grade level and lying left and right, and not get completely laughed at and called out? Hey, yes we can! Can we slash taxes for the rich and not the poor! Yep – they still just think it’s “tax cuts”! Can we get rid of social programs, environmental protections, government oversight of business? Yep! Can we just go along with the crazy ex-POTUS lying that the election was rigged against him? Looks like! Can we incite them to storm the Capitol! Yep! If we tell them it was “Anti-fa”, will some of them believe it? Yup. Hey, let’s see if we can have maniac Q-Anon believers in Congress! No problem. Gaetz was running a pedophile racket – let’s see how long it takes him to get ejected from Congress… well, not yet! Hey, look, all this noise it great at getting people not to notice what’s really going on… yup, how many billions have you got now? Oh, lots…