I don’t get it either, honestly, and I’ve lived with it all my life. Mostly, AFAICT, it’s a combination of four things:
- Disproportionate political influence of rural areas, which tend to skew conservative.
- Profound political and cultural legacy of slavery and racism, which has left a lot of residual fear and distrust among conservative white (“post-Confederate”) Americans. Demographic trends towards future “majority-minority” racial composition are making a lot of those folks nervous too.
- Serious political irresponsibility and corruption, primarily although by no means exclusively among Republicans, which has limited political transparency and allowed major donors to call the shots on policy for their own benefit.
- A post-seventies wave of right-wing rage about being systematically wrong about nearly everything, to the point that many of them are willing to reject democracy, reason and facts for no better reason that than it “triggers the libs”. Factors (1), (2) and (3) all exacerbate this part, of course.