From what I know about fundamentalists, evangelicals, they are fanatically DEFENSIVE. They've always seen the outside world as a menace, a threat. And so their core beliefs are centered around resisting it. "Resisting temptation," and rival churches. There is good, and there is evil - and nothing in between.
So more than any other believers, they've resisted change. At least on the official record.
And oddly? Their remarkably flat percentage is almost exactly the same, as the also VERY consistent number as those who approve of Trump.
I think it has to do with always seeing your group as threatened constantly; and having systematically setting up strong defenses from the beginning. And therefore being utterly convinced ... and strongly resistant to anything that seems to disprove their religion. Being ... immovable.
Something similar to fanticism. And? Maybe reflective of some kind of almost permanent, perennial underclass?
Those are all incredibly, remarkably, unbelievably straight lines, in any case, for a graph.
SOMETHING is going on.