But they don't wind up in the news that often, especially non-chiefs. Once the confirmation process is done they become rather anonymous, really when was the last time Alito made major headlines? He got sworn in 6 months ago, I think he's written a few decisions or decensions and that's been it. Remember also what you're looking for is backwards name recognition, probably a lot of the people who couldn't remember the names cold if you listed off 6 names, two that were justices and 4 randoms could pick out the right two. There's an easy excuse for not knowing the branches of government: how does it really effect you? Do the labels legislative, executive and judicial alter the daily life of the average person? Given that none of them are limited the way the founders designed anymore, they all over step their bounds, and how little control we actually have over any of them, it really doesn't impact the average life of the average person.
What they're going to be voting for is a career politician, someone who is inherently a whore and a liar, who might or might not actually do the stuff they say they will, who might but probably won't limit themselves to what the founders say their job title should be able to do. Honestly it's a nerds vs non-nerds thing. There are news nerds who also tend to be government nerds, they pay attention to all this stuff and know a lot of names and definitions. But just like with any other brand of nerd they're the minority and spend a lot of time on stuff the rest of the world doesn't consider important or interesting. I'm a nerd, I'm many different types of nerd actually, including a news nerd which is why I spend so much time on news websites like FR. But I recognize that most of the people aren't nerds, and for most folks the three branches of government have no more direct impact on their daily lives than the 3 breeds of Klingon. Congress is no less filled with crooks and dipsticks if you don't know they're the legislative branch and what the limits of their power are supposed to be than if you do, and one way or the other you only get to vote for 3 out of 540 so you really don't have that much say.