I have a lot of thoughts about this which I won't take the time right now to share.
But I think Dad04 hit the nail on the head.
In HS, upper 80s and even 90s lets you get away with a lot of bad pitches. Bad fastballs that a HS hitter is just trying to survive and chases. Bad fastballs, down the middle of the plate, that most HS hitters can't handle. And bad breaking balls, in the dirt, 2 feet in front of the plate that the hitters will also chase because they committed early in their swing to try and handle the fastball.
Most of those advantages for pitchers that go along with speed in HS go away most of the time in college.
Yes, velocity will likely increase some...but its gaining command of 2-3 pitches and in particular pitches #2 and #3 that makes a good college pitcher.
I believe that is the focus of the coaches for most pitchers entering college baseball.