Then he would know how NBA ready he is and if/where he will be drafted. Weigh that against another year at BYU. Compare the benefit of another year of development and the money he would earn either way.
Seems like he would be better off with another year at the college level, playing in the Big XII and gaining skills and recognition. Improve his NBA draft position maybe.
But he makes the decision and does what he thinks best. Maybe he'll do well.