The top programs stay on top because they get the top tier talent. The top tier talent are the few girls that you notice within the first 15 minutes of a game typically. Those girls just move and play different. It doesn't take many looks to make a group of tier 1 talent if your a coach at a top program. The tier 1 players can come from any club. It's the role players or glue girls that get the benefit of the doubt at the top clubs. The college coach know those girls can play at a fast pace and get the ball to the "talent" like they did at their club team. Some of those girls pop when given a new opportunity at college.
If you are not special around a group of decent high school caliber players, why would a college coach take chances when his/her job depends on it?
It's not hard to quickly pick out the top girls across the country and they are correctly placed on the UA and AS teams. Those teams miss on a few girls, but generally on point except to the parents of the girls left off those lists.