Incorrect, everyone but maybe 1-2 on that list of 20 improved in College, but maybe no one became All Americans etc. I think your perspective isn’t realistic thinking a strong High School team is also producing numerous Division I All Americans. Fact is All American talent is very special and is only because of coaching to a certain extent. Most are just one off talents from average High School teams.
Add up how many High Schools there are, how many High School runners, and then how few run in college and how few become All Americans. Southlake Carroll may consistently be Top 10 Nationally, but how often have they had individuals top 10-20?