He showed no consistency, if he goes 1 good 1 bad again, do you think they are going to trust him going forward for the rest of the year? He had 10 starts before going down, 5 good and 5 terrible. They want consistency, he's had 2 pretty good starts, a 3rd will show he's trending where they want him to.
Edit: This has nothing to do with him becoming a successful MLB starter, it's about winning games and putting the best people out there to do that right now.