I hate to say it but the majority of the FASTEST guys I have been around in high school and college campuses did not have great work ethics. They have great gifts but did not demonstrate the best numbers on the platform or the power rack.
The next tier of kid usually had the best combination of explosive power, nice squat numbers (1.5-2.5 x bw squat) respectable power cleans..... I believe there is a point of diminishing returns in terms of what a weight room will give you on the track or field. The starting 22 at the University of Nebraska back in the 90's were not the strongest guys in the weight room BUT they did have nice strength and wonderful v.j., 20 yard dash and 5-10-5 composite scores.
I think it's a blend of DNA, good relative strength, and technique coaching.