You need to remember that a lot (probably the majority) of these people have been overachievers since they were kids. Pushed by their family, mentors, etc.
They know that in order to get to the top, you need to play the game - it's exceedingly rare that one just stumbles into the top, by intellect alone. There are tons of smart kids out there, you need some edge.
So they pick up extracurricular activities, join clubs and boards, start making a name for themselves. Get letters of recommendation, and what not.
Now they're suddenly students at top schools, with like-minded peers around. They start chasing internships, and it's the same thing all over again. Join the best clubs / orgs, get leadership experience, etc.
For these driven "type-A" folk, it's always about hitting the next milestone. It never ends. Get into best prep schools, get into best universities, get the best internships, get the best jobs, get into the best business school, get the best post-MBA job, get the best promotion, etc.
It's like a professor told me once: Some of the brightest students, academically speaking, do not necessarily end up with the best jobs or positions. A lot of them tend to be too focused on their academic work, to the point where they neglect things like resume-building, networking, interviewing skills, etc.