If you are comparing public radio news and information stations to commercial music format stations that's one thing. If you compare the audiences for public radio news and information to commercial right-wing talk then you see a significant different in the respective audiences income, education levels and in other lifestyle factors.
"Smart" and "dumb" are vague terms and almost impossible to quantify. Public radio news and information content is more intellectually demanding and therefore draws people who appreciate such content. Right-wing news talk is largely hate speech and demagoguery and draws a different kind of person.
Some music formats have audience demographic profiles similar to public radio news and information (and often many of the same listeners). Other music formats do not.
People who don't appreciate intellectually-demanding content tend to resent those who do appreciate it. Ask any kid with good grades who got beat up at recess. Guess which listens to public radio and which listens to Rush.
You make it sound like NPR programming consists of calculus equations and nuclear physics discussions, when most of it is just dry news reporting, along with a few arts oriented features. It's really not that intellectually demanding. Just drier delivery.