Okay, a little less rant this time, but don't you see? The only reason we even *ask* about these kids is because the great hs coaches brought them to a level of State/national prominence!
I can't find the stat, but I've read that fewer than 10% (actually, I'm pretty sure it's fewer than 5%) of all hs athletes compete at any college level for even a single season. Of course, a majority simply don't have the talent and/or don't go to college at all. But for every hs kid that a good coach brings to prominence, there have to be 10--I'd say more like 20-50--with similar talent who attend the crappy-program schools and don't get coached anywhere near their potential. In fact, most of them don't get coached at all, because the coaches don't get them on the team.
The percentage of super high school kids who later move on to world-class competition is going to be minuscule in any case: world class is incredibly rare. For sure, the ones who were never motivated to be on their hs team aren't going to do it. So how should we judge the coaches of the super kids? By how many (percentage, if not absolute) kids they produced who were super *in high school*. Those are the coaches who at least gave their athletes the chance for later international greatness--a level that perhaps one in a thousand will reach, in any case.
One example, then no more screeds (on this topic, anyway). A guy who runs 9:00 for 3200 in high school is terrific, right? Yet if, years later, he is somehow fortunate enough to carry that pace for 10,000m--more than triple the distance, a *fantastic* improvement on his prep mark--he's a low-28 10km runner: (American) national class, for sure, but more than a lap behind the fastest men in the world, and without a prayer of medaling in a world championship. So I guess the high school coach who brought him to 9:00 burned him out, right? Right...
The kids you're asking about (re: "where'd they go?") are, with *very* rare exceptions, those whose high school coaches did their job correctly.
Which is why you're asking about them at all.