its the same in a lot of sports a lot of good football and basketball players just happen to go to long beach poly, mater dei etc. a lot of good wrestlers just happen to wind up at blair in new jersey, graham in ohio, apple valley in minnesota. berkeley high school had incredible amount of talent in track in the early 1980's (a dozen kids under 48 for 400 for example which is more than most division 1 schools.
really what probably happens is the parents see or are told their kid has talent, so they arrange to transfer their job near a high school with a good program, so the strong get stronger for a while, then the coach leaves example long beach wilsons girlstrack coach last year, the muir coach in track in the 1990's, the berkeley track coach in the 1980's, and then the program usually falls apart, not always.