I think they have been carefully selected over the years as fully indoctrinated believers. The difficulty is when they get to the top, they see how it all really works.
But, as full believers, they justify and rationalise this. I have seen this operate in people who have climbed the Political ladder, they may still be "believers" in the ideology they espouse, but realise it is pragmatic to lie to the "faithful" by not telling the whole truth, or downright telling porkies. But, the said politician STILL believes !
So, with the position, must come increased cognitive dissonance, but they have had a lifetime of dealing with that.
Deluded Charlatans are still Charlatans.