Business is a very particular discipline in its own right. While the technocrats and bureaucrats of corporate America's professional management and executive corps have certainly done enough to exaggerate its exclusivity and idiosyncratic character, the fact remains that it's a rather distinct kind of thing. The qualities that make one a good programmer, a good technologist, a good innovator, etc. aren't necessarily the same qualities that make one a competent or happy business owner, especially when, as a matter of practical necessity, much of the everyday workflow is tedious administrativia or other things banal to engineers.
I'm all for the idea that intelligent, confident and well-rounded people are better off doing something more interesting than fighting mediocre fights in the cubicle trenches, but that doesn't mean they're all--or even a majority of them--are entrepreneurially disposed per se.
Plus, as has been pointed out elsewhere in this post, joining early often brings equity with it, which, from a certain point of view, is quite an entrepreneurial proposition.
If nothing else, it's simply not mathematically possible for everyone to be the chief in the driver's seat; many technical endeavours seriously require people to build out and scale.