I was talking to a neighbor the other day about the far right's anti-everything stance. I noted how the GOP didn't used to be like this. She thinks their current intellectual decline started with Reagan, who courted the religious nuts into the party and dumbed it down. If it isn't in the Bible, then it's wrong.
I don't know if she's right or not, but it does sound like at least one reason why they can't accept new ideas. Climate change denial is merely one manifestation of this.