He’s about 24 years old. At that age, he’s not going to increase his draft stock. If anything, teams next year might see a 25 year old as significantly less valuable than a 24 year old because he’s lost a year of his athletic prime. That might cause him to get drafted later.
He was planning on going pro after last year, but decided to come back after injuries hurt his draft stock last year. This year his draft stock is as high as it’s likely to get, and having him drafted higher is good for BYU.