Its a margin of how you define successful. If you look at the numbers a person who joined FIRST as a junior in 1992 (that gives them at least 2 years in FIRST), that person would be 30 or so right now. Barring any of the google-type guys, if you look at most company leaders and so-called "big-shots" they are all 40+, so possibly we just need more time
.
The other issue, is that the engineering path isnt often, these days, the path to amazing success (in terms of money or fame). Yes you make plenty of money, yes you come up with cool new things, yes you have an awesome job (so you really are successful by my definition), but 80% of the time, engineers take the technical path, not the management path, so you become a great engineer, but not the president of a company.
The other thing is that sooo many of the really involved FIRSTers have gone on to either start new teams or get involved with their old teams... that many of us spend so much time doing FIRST, that we dont have time to develop great new inventions (outside of work) or start our own businesses, or make plans for world domination(jk
).
So my take is that there are probably many reasons why... but again, it very very much also depends on how you define "highly successful", I was assuming the comment above was in regards to money & fame.