Why do we believe that intelligence and nerdiness go hand in hand? Not to be all anecdotal or anything, but the top 6 GPA ranked people in my high school class

Why do we believe that intelligence and nerdiness go hand in hand? Not to be all anecdotal or anything, but the top 6 GPA ranked people in my high school class were normal. They weren't popular, but they certainly weren't nerds. I was 7th, and I didn't really count as a "nerd" until college, when I started going to anime club. In high school, I was so socially awkward that even the nerds wouldn't let me play DnD with them. The nerds were all kind of middle-of-the-pack intelligence. I suspect that we believe this because there are some powerfully intelligent and powerfully nerdy folks out there. But if you just look at academic performance, I bet the reality isn't so strong. There are a lot of dumb nerds out there.