There are 130 FBS teams. How would you even begin to organize a high school draft in a way that was presumed to be fair to every team? Even if you just take the power conference schools it's still twice as many teams as the NFL.
Or how do you make it fair to players who really do want to stay close to home and play for an in-state school?
"Sorry, Mr. Three-star Offensive Guard from Raleigh. I know three generations of your family went to North Carolina State, and you wanted to play there and they wanted you to play there, but Utah State took a flyer on you in the 84th round of the draft. Whaddya gonna do, you know? Now pack up your shit and fly across the country for spring practice."