alt Hacker NewsThat could simply be explained by early high achievers being worked hard by their parents or something else while people with innate abilities making progress slower (because most people are not overworked). For the first group they sizzle either because the pressure is removed as they grow up or because they hit their ceiling.
My experience is almost the inverse of what you describe, I never had to work at all until university, I was a top performer until "physique 1: mécanique newtonienne" it was the first time (and the last) I failed at something academic.
That was quite a shock to realize that I had to do the exercises and the homeworks if I wanted to pass. And since I was not use to efforts, I was no longer the top performer in classss where you have to do the exercises to really understand the matter.
I was recognized as extremely clever by teachers and other students but let me assure you that over long enough, discipline (witch I don't really have) and consistent efforts beats cleverness.