He is up against a REALLY low inning count this year. If you were to start using him as a starter today, you'd lose him for the year by about July. The Sox made the decision that they can get him his innings AND be able to use him to benefit the ball club. He was never going to be a starter this year because of the fact he has never thrown a significant amount of innings in a season. His high IP in college was 65 innings, so you are probably talking about 100 inning top, MAYBE 120. Even Chris Sale got 103 college IP, plus another 33 in the minors and Chicago before he got to the bigs, which is DOUBLE Crochet.
They were never going to use him up by July, either in the minors or the majors.