Here in IL, I know for a fact from talking to some college coaches that a kid who doesn't play for their HS automatically causes a red flag-no matter HOW GOOD the kid might be at baseball. Now, this doesn't mean that they won't take a chance on a kid, but it causes some additional concerns.
Many have posted on here in other similar topics with the reasons I heard these coaches give to me:
1. HS baseball develops a true sense of "team" more times than not over a summer/alternative/showcase team. Not ALL the time, but most programs. (playing with the same kids, progressing together as a unit, knowing the kids on and off the field for extended periods of time, etc).
2. Learning to structure their life with baseball, school, responsibilities, etc-preparing them for college and adult life.
3. If a kid leaves his HS program because it's bad for a "grass is greener" chance somewhere else, what might the kid do if the college program has 2 awful seasons and/or the kid doesn't start? Might he leave? College coaches consider this.
Obviously this is just what I've heard from some IL coaches, and I know the landscape of things is different in other parts of the country.
My personal take too: playing for a HS state championship, making history for town/school, and being remembered by an institution FOREVER is worth it over showcase.
I am firm believer in that HS ball AND travel/showcase is necessary to further a dream-if that dream is for a kid to play beyond HS.