In addition to what everyone else saisd, I think there is the issue of making the athlete robust enough to handle the high-intensity and specific training.
I recall an audio interview with Pfaff where he talked about one of his sprinters who was, as he put it, allergic to iron. Pfaff apparently felt that the lack of weights in the program were part of why that sprinter often got hurt.
High intensity sports include a lot of pounding to the body, joints, connective tissues. Weights earlier in development strengthens those and could be beneficial from that standpoint as well.