It is not hard to be a great high school player when you are a head taller than most of the players that guard you. In D-1 he might still have the inches, but everyone he plays against will have 50-60 lbs on him (his MaxPreps entry says 7'0" 145 lbs).

BYU has consistently been able to get stiffs with great height to come to BYU and consistently these players have been bullied by bigger, stronger and/or more athletic big men. I wouldn't even consider giving him a scholarship over Kyle Davis.

Consider the following BYU case studies:
James Anderson (6'10"):
McDonald's All-America nominee from Arizona. Named first-team all-state, the Grand Canyon Region Player of the Year and the Navajo Times Four Corners All-Area Player of the Year. Averaged 17 points, nine rebounds and six blocks per game and set a state record with 14 blocks in a game.

At BYU he averaged about 6 minutes per game and less than 2 points per contest. Opted not to play his 4th year of eligibility.

Luke Worthington (6'10"):
McDonald's All-America nominee (one of 7 in Wisconsin). Named Wisconsin Basketball Coaches Association Division I All-State Honorable Mention. As a senior was a team captain and averaged 13.6 points and 10.0 rebounds per game.

Despite starting 21 games and playing in 33 (around 12 minutes per), Luke grabbed just 55 total rebounds and blocked 2 shots while committing 93 fouls.