I have not read through this thread much, but an under-appreciated element is what is called selection bias. The individuals that catch your attention are those that have done quite well in high school. These runners tend to: 1) have been lucky with injuries that last year or two in high school; 2) have made bigger improvements than most; 3) have matured earlier than many; and 4) been more (much more?) motivated than most runners; and 5) had better coaching than most high school runners.
So, we may be seeing more injuries than in the past (especially because the work load generally increases, but also because some injury issues take a long time to develop). Their coaches before were focused most on these select runners, but now that are but one of many runners. Related to this is that the runners are no longer getting quite as much positive feedback (used to be superstars, now that are just one among many, especially in top programs). etc.