It's because everybody, republican voters included, understands that republicans are extraordinarily stupid and their policy does not work.
If you look at Trump, the only people who think he's honest are his opponents. His own supporters swear up and down he's a liar, he doesn't know what he's talking about, he won't do this or that. And this is their defensive! These are the best arguments they can articulate in his favor!
I think, the thing is, a lot of people don't want effective leaders or care. They want to win, or maybe they want to screw over some people they don't like. So go ahead and elect the idiots with bad policy, because government sucks anyway or something.