Because... they're dumb?

So that is easy. Religion is based on tradition, and the right is heavy based on religion. Tradition is all about doing a thing without really knowing why. So it skews heavily toward the non-critical thinkers.

Most have ability to learn more, but the systems indoctrinate them not to learn more than they allow and be obedient, they go along to fit in, their team wins when others lose, zero sum thinking. It's damaging and holds us all back.