On the NCAA site, there are 299 D1 baseball teams listed. Using an average of 15 pitchers per team, that is 4,485 guys pitching at the D1 level in any one season. Just looking at the class of 2017, 292 RHP's threw 90 plus and 270 LHP's threw 85 plus(from PG site). If you expand the parameters on the PG site to 2017 RHP's throwing 88 plus and LHP's throwing 84 plus, the list expands to 621 and 440. I don't know how many of those players signed professionally but I'm guessing that number is close to how many were unaccounted for, leaving approximately 1000 pitchers above 88 and 84 available for D1's to recruit from HS. Mix in JUCO's that sign D1 to pitch and that doesn't leave much room for guys below those thresholds to catch a coaches eyes, even if they are fully capable at competing at that level. Fortunately, it does happen from time to time.
Feel free to challenge my math on this, I won't get offended. I looked at three D1's and two had 16 pitchers and the other 14, hardly a representative sample of all D1's. Would also like to know how many 2017 HS pitchers signed professionally out of HS?